Is there any big deference between topspice and LTspice, is ltspice enough or not?i am looking for good software to help me to do simulation for switch mode power supply design

 

I'm not familiar with topspice, but it is all about the models. If you have the models you want to use for the simulation then either one should be fine. LTSpice is free and has a large Yahoo Support Group that you can get counsel and advice from. You could just run the experiment and tell us your results.

 

LTspice was created primarily for SMPS design.

 

As PB noted, the main difference is likely the available models.
Check to see if either has the models for the devices you want to use.