Conventional STAP algorithm can place notch adaptively in the direction of clutter. However, due to the time lag of adaptive weight, data mismatch may occur. Therefore, a approach is presented which can wide the notch. The new method constructs a temporal decorrelation matrix which is used to modify the clutter space-time covariance matrix and get adaptive weight. The new approach forms notch which width can be modified centered around the clutter direction, and the increased computation complex is little. Performance analysis is carried out using simulated data as well as measured data from Mountaintop experiment. The numeric results show good agreement with the proposed theorem.