The invention belongs to the technical field of program compilation, in particular to a predicate-based automatic parallel optimizing method. The method mainly comprises the following: (1) a step of predicate establishment, which is to establish a parallel predicate of a program by using different kinds of known information of a user program, and remove simple dependence of the program; and (2) a step of parallel loop structure establishment, which is to perform subsequent parallel analysis and judge whether to use the parallel predicate or not under the restriction of a predicate condition. The parallel predicate establishment is based on the traditional array data flow analysis and loop dependence test. The loop simple dependence caused by imprecise loop information is eliminated through predicate establishment, so that the analysis range and the parallel optimization effect of the traditional automatic parallel optimization are widened and improved respectively. In the actual execution of the program, if the predicate is not satisfactory, the program executes the original serial version and the increased judgment operation and skip operation hardly influence the overall performance of the program; and if the predicate is satisfactory, the parallel version of the loop structure is executed, thus the program performance is obviously improved.