Utilizing the orthogonal feature of space time block coding ( STBC) ,  a simple and feasible algorithm based on constant modulus (CM) criterion is proposed for blind multi-user detection in STBC MC - CDMA systems. The algorithm proposed in the paper as a simplified version of the algorithm based on the least square constant modulus algorithm(LSCMA) has the advantage of half taps and therefore considerable reduced computation at the cost of a certain loss in performance.