调用方法：
 public string ConvertToChineseNumber(string old)
        {
            Chinese ch = new Chinese();
            long num = Convert.ToInt64(old);
            string re = ch.returnResult(num);
            if (re.StartsWith("壹拾"))
            {
                re = re.Substring(1, re.Length - 1);
            }

            return (re);
        }

完整代码
using System;
using System.Collections.Generic;
using System.Text;

namespace Public
{
    class Chinese
    {
        public string returnResult(long num)
        {
            string numStr = num.ToString();
            if (numStr.Length > 8 & numStr.Length < 16)
            {
                string[] firstSplit = new string[2];
                firstSplit[0] = numStr.Substring(0, numStr.Length - 8);
                firstSplit[1] = numStr.Substring(numStr.Length - 8, 8);
                string result1 = getString(firstSplit[0]) + "億";
                string result2 = getString(firstSplit[1]);

                return result1 + result2;
            }
            else
            {
                return getString(numStr);
            }
        }

        public string getString(string str)
        {
            if (str.Length > 4)
            {
                string[] secondSplit = new string[2];
                secondSplit[0] = str.Substring(0, str.Length - 4);
                secondSplit[1] = str.Substring(str.Length - 4, 4);
                string result1 = getRe(secondSplit[0]);
                string result2 = getRe(secondSplit[1]);
                if (!secondSplit[0].Equals("0000"))
                {
                    result1 += "萬";
                }

                return result1 + result2;
            }
            else
            {
                return getRe(str);

            }
        }

        int[] value = { 1000, 100, 10 };
        public string getRe(string doWith)
        {
            char[] number = doWith.ToCharArray();
            int length = number.Length;
            string re = "";

            for (int i = 0; i < length; i++)
            {
                switch (number[i])
                {
                    case '0':

                        if (re.EndsWith("零"))
                        {
                            re += "";
                        }
                        else
                        {
                            re += "零";
                        }

                        break;
                    case '1':
                        re += "壹";
                        break;
                    case '2':
                        re += "贰";
                        break;
                    case '3':
                        re += "叁";
                        break;
                    case '4':
                        re += "肆";
                        break;
                    case '5':
                        re += "伍";
                        break;
                    case '6':
                        re += "陆";
                        break;
                    case '7':
                        re += "柒";
                        break;
                    case '8':
                        re += "捌";
                        break;
                    case '9':
                        re += "玖";
                        break;
                }

                int index = (int)Math.Pow(10, length - i - 1);
                if (number[i].ToString() == "0")
                {
                    index = -1;
                }
                switch (index)
                {
                    case 1000:
                        re += "仟";
                        break;
                    case 100:
                        re += "佰";
                        break;
                    case 10:
                        re += "拾";
                        break;
                }
            }

            if (re.EndsWith("零"))
            {
                re = re.Substring(0, re.Length - 1);
            }
            return re;

        }
    }
}