I'm 16 and play basketball and is doing well in it but there is always a negative thought in my mind disturbing every time that I can't cop with studies but I'm doing very well.Help me to put the end of this negative thought

You need to be clearer. Explain more please.

Thanks for suggesting
I can explain this as a hindrance in my progress.Whenever I achieve anything there is a always a fearing thought of loss and I can't believe on myself,on my strength.

I strongly suggest you speak to a counselor or therapist. Its not uncommon for people to feel they will always fail no matter how often they succeed. But a good therapists can help you with those feelings. Talk to your school's guidance counselor for a recommendation.