//将数据添加到搜索范围
this.comboBox1.AutoCompleteCustomSource.AddRange(new string[] { "10.152.154.89", "10.152.154.90", "10.152.252.10", "10.152.252.11" });

this.comboBox1.AutoCompleteMode = System.Windows.Forms.AutoCompleteMode.Suggest; 
this.comboBox1.AutoCompleteSource = System.Windows.Forms.AutoCompleteSource.CustomSource;

 private void comboBox1_TextUpdate(object sender, EventArgs e)
        {
            ComboBox cbBox = (ComboBox)sender;
            List<string> listNew = new List<string>();
            cbBox.Items.Clear();
            foreach (var item in listCell)  //已有数据
            {
                if (item.Contains(cbBox.Text))
                {
                    listNew.Add(item);
                }
            }
            cbBox.Items.AddRange(listNew.ToArray());
            cbBox.SelectionStart = cbBox.Text.Length;
            Cursor = Cursors.Default;
            cbBox.DroppedDown = true;
        }