Hi doctor, i have mild tinnitus. i'm thinking of using noise cancellation headphone. will this worsen my tinnitus?

Depends.: The key with tinnitus (ringing/noise in ears) is to try to mask it with background noise. Simply put, it becomes harder to hear the tinnitus against more background noise. If you use headphones to listen to low level music/sound, then tinnitus is improved during this since it gets masked. If you simply cancel out all ambient noise resulting in silence, tinnitus becomes more noticeable instead.