i got solution here is the one...
Devexpress combobox control have default maskBox in it which can provide the auto suggestion feature similar like .Net defult Combobox control.
Here is the sample which works for me to show the auto suggestions...
comboBox1.MaskBox.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
comboBox1.MaskBox.AutoCompleteSource = AutoCompleteSource.CustomSource;
comboBox1.MaskBox.AutoCompleteCustomSource = colValues;
c
omboBox1.Properties.Items we can for drop down items of combobox