This paper presents a method of how to select the equipment condition monitoring objects and parameters of complex system equipments. The method determines the condition monitoring objects and parameters from the two levels of function and components. At the functional level, the monitoring objects and parameters of the system are identified by using the method of funtion-based-fault mode and effect analysis (FMEA); at the component level, FMEA and risk analysis (RA) are used to ascertain the Maintenance significant items (MSI). Then, we use Analytic hierarchy process (AHP) method to determine the priority order of MSI. This paper takes the on-board equipment of train operation control system as an example. At the function level, on-board equipment can be divided into six functional modules and the condition monitoring parameters are determined by using the method, funtion-based FMEA. At the component level, eight MSI are selected based on the results of FMEA-RA and the priority of these eight MSI is finally determined based on AHP, which lays a foundation for condition-based maintenance (CBM) of complex system equipments.