This paper describes a new control algorithm for a transversal filter in a cross polarization interference canceller (XPIC) for digital microwave radio systems. The proposed new algorithm includes the shift bit select (SBS) method whose abjustment function of optimal correlation provides complete adaptability to the severe propagation condition changes. High speed control response under fading, as well as stability under steady state, can be achieved. Moreover, by combining the SBS method with the maximum level error method, wide acquisition range and short acquisition time can be realized. An analysis of convergence properties of the XPIC is presented, and using a 256 QAM signal, the availability with the SBS method experimentally confirms the superiority over conventional algorithm.