The accuracy of the data dependence analysis of a client program will decide in what an extent the compiler can unleash the power of the potential parallelism of the client program. Most of the current works on dependence analysis are based on the dependence equation and constraint inequalities of loop variable bounds ( sometimes augmented with the direction vector ). Unfortunately, they can not give an exact detection on the dependence which may greatly affect the parallel optimization of the client program when software pipelining technique is employed. In the paper, we give a more effective constraint inequality which could reflect the characteristics of software pipelining technique and will improve the power of dependence analysis of most of the current algorithms when applied to software pipelining.