Recently I formatted my lap.  After that my liquify tool is lagging. Before that, it worked well.  Anyone knows how to fix it?

Thanks in advance!

It is pretty vague without know what your hardware is, what software you are running on it etc - things which Adobe support would ask you.

First thing: Check if you have disabled GPU for Liquify (by holding Alt key when selecting Liquify filter).

Try with a lower resolution image. If it is still lagging - try a different (newer) Photoshop version. In earlier versions there was a problem with high resolution images and lagging and we sometimes had to work on a lo-res version, save the liquify mesh and apply it on the hi-res.

Don't forget to check carefully all your settings - for video driver and Photoshop. Just in case there is something there. If by any chance you are running software that eats system resources - that might also interfere with what you are doing.

Sorry but without info about your hardware and the software running on your computer this is just generic advice. If you want specific help you might want to contact Adobe support.

Is any AntiVirus software running?   
         Every file will run through that to be scanned if it is not disabled.. There might be settings to ignore certain file types.

Unplug your USB drive when using liquify...