I use the code below to change the display format of one column so the decimal only display two numbers after the dot, but it didn't work. I also use the design models to set the format property of one column, again, it didn't work. Is there any reason?
ultraGridZYYWSR.DisplayLayout.Bands[0].Columns["percent"].Format = "##0.###";
Just a wild guess due to the name of your column. To format a decimal number in infragistics neatly as a percentage set the Format string to "P".