The adaptive detection problem for mismatched useful signal is considered. A novel parametric adaptive detector is proposed, and the adaptive matched filter and double normalized adaptive matched filter are the special cases of the tunable detector. The detector parameters can be used to control the detection performance for slight mismatched signal and rejection performance for serious mismatched interference. The probability of false alarm and the probability of detection for mismatched signal are derived. The computer simulation results show that we can choose suitable parameter to control the ability to detect mismatched useful signal and the ability to reject interference.