Bogie condition monitoring is the main object of passenger car running safety monitoring system,and it also is the difficulty of monitoring job.Because of bogie structure and diversity of vehicle running environment,bogie's dynamic characteristics are complicated.And it's not accurate to use the same standard parameter to judge a bogie's performance.Taking Absolute and Relative method,comparing historical date of one bogie and date of all bogies in one train,we can diagnose bogie's running state and its trends effectively.