A new decision-directed cost function （criterion） for blind equalization proposed by Daoben Li and Proakis is firstly introduced in this paper. The cost function can simultaneously force the error probability as small as possible and the overall channel’s impluse response function as close as possible to a desired one（full or partial response）.The least-square algorithm which adopts the above cost function is also intreduced. Simulation results demonstrate the effectiveness of the algorithm.