I have done BCA but I can't get perfect job from that so If I join NIIT for professional training pf 6month how successful it will be?

With NIIT you will certainly stand to gain more than what you were with mere BCA Priyanka. But then learning is one thing and application of it is another thing which you need to do very skillfully to succeed in a job. I suggest that simultaneosuly you must also enhance your other abilities such as