This paper presents that the order ratio aliasing and leaking are two main problems of signal processing in the signature analysis and discusses the reasons for the order ratio aliasing and leaking. The paper presents that the order ratio filter (ORF) is a good method of restraining order ratio aliasing. The frequency ratio synthesizer (FRS) is developed for restraining leakage and engineering applications. The ORF and FRS are the main hardware devices in the whole signature analysis system in a microcomputer. The paper gives the design principles，circuit block digrams，system block diagram of the signature analysis system in a microcomputer which is composed of the FRS，TMS32010 data acquisition device，master computer and plotter. Finally. the results of fault diagnosis using the system to a ball bearing are given.