>Dear Bruce,
> Thanks for your idea. I need to examine in details under what circumstances the slow down occur. I am a junior in VFP. I have no idea the meaning of vfp coverage Log. How to run it?

Sorry, been away. Perhaps others have steered you in the right direction. Still, the Coverage Log is the best overall way to locate bottlenecks, and is simple to use. In the development environment, put this code before you build and run your app. This is covered somewhere in vfp Help, I believe:

1) SET COVERAGE to c:\mycover.log (to start the log)

2) Run all the code with problems...

3) SET COVERAGE TO (to end the log)

Now, go open c:\mycover.log, and check out the lines of code where the slow (largest) times are located. It often is SQL that is responsible for bad performance, but may be any number of other things, like form/pageframe loading, grid/list/combo loading, LOCATE without index, etc.