Abstract: Risk Priority Number(RPN) method in the failure analysis is the hotspot of research at present.Because of the defects of RPN and complex mix-reasoning of the failure in the mechanical system,RPN method may lead to wrong decision when it used to the mechanical system failure analysis.Based on the study of defects in the RPN,put forward the ERPN method based on the economic loss.This method put the severity which has strong subjectivity in the qualitative analysis,using the economic loss which reflects the failure effect more accurate instead of severity,improves the probability analysis and put forward a new formula for the priority number calculation according to the mix-reasoning of the failure in the mechanical system.ERPN method is expected to improve the RPN and the analysis results could be more objective.

Key words: failure analysis, priority number calculation, economic loss, risk priority number