Hi mrinal0308,
These types of fluctuations in score can be due to a variety of causes. While the 'obvious' answer is that you're likely making more/fewer little mistakes on certain Tests than on others, there are a number of other factors to consider. Thus, we need to start by defining how you took each of these CATS:
1) On what date did you take each CAT?
2) Did you take the ENTIRE CAT each time (including the Essay and IR sections)?
3) Did you take them at home?
4) Did you take them at the same time of day as when you plan to take your Official GMAT?
5) Did you ever do ANYTHING during your CATs that you couldn't do on Test Day (pause the CAT, skip sections, take longer breaks, etc.)?
6) Did you ever take a CAT more than once? Had you seen any of the questions BEFORE?
Thankfully, the GMAT is a consistent, predicable Exam, so you CAN train to score consistently at a higher level.
GMAT assassins aren't born, they're made,
Rich