Exercising squats is good if you have knee injury? or it will worsen the injury?

Depends: If the injury is to the front of the knee (patella area) squats can actually increase the pain. It is best to start with isometric exercises ( where the muscle is tensed against resistance and the joint does not move, followed by pain free arc exercises. Your doc or physical therapist is best to advise your on a specific regiment to follow your your specific injury.

Dont go deep: Deep squats may cause inc pain. Don't squat too deep.