Abstract: To overcome the great correlation peak fluctuation caused by the composite matchedfilter prepared with conventional synthetic discriminant functions, the conversion process of coding from conventional synthetic discriminant functions to the coding matched filter is analyzed. The reason for correlation peak fluctuation was found. A modified scheme, in which the coding arithmetic is considered when the linear combination coefficients of the synthetic discriminant functions are calculated, is proposed. The results of the computer simulation indicate that, compared with the conventional synthetic discriminant functions, this improved method can greatly reduce the correlation peak fluctuation of the composite matchedfilter, simplify the postprocessing and improve the veracity of the automatic identification of the correlation peak.