Abstract: In most application programs the execution of loop occupies a large proportion.Software pipeline is one of the most effective methods for loop optimization.DESP （decomposed software pipelining） approach uses LDDG to describe loop data dependence,and LCDG is added to describe loop control dependence.By combining LDDG with LCDG to form LD ＆ CDG,a new way for loop with conditional branches is presented.In addition,through the improved list scheduling algorithm,a solution for the multi cycle execution operations in a loop is proposed.Finally,a VLIW machine model is designed,on which the improved DESP algorithm is simulated and shown to be correct.