After two weeks' work, the problem finally resolved. There is indeed a bug in controling keithley2303 in ke230y_32.dll file.
The file ke230y_32.dll's location is: C:\Program Files (x86)\IVI Foundation\VISA\WinNT\Bin\.
Source code also can be obtained from that place.
Because the instrument is a single channel power supply, it cannot distinguish a command with such word "CHANNEL1".
In the end it respond an error from instrument when getting a parameter named "CHANNEL1" through MSR.vi in Labview.
The sollution is simple enough, we do not need to modify the dll file. Only thing we need do is to set the parameter of channel name in MSR.vi from default string "CHANNEL1" to empty string.
Such a simple operation spend me almost a week time, I feedback the result here suppose to help the others who stand in the same position with me.
Thanks again to the upstairs guys' help, it really helped me!
