Abstract: This paper is mainly concerned on problems of optimising the preventive maintenance(PM) interval of equipment given inadequate inspection data at PM. Firstly,a PM model is proposed to describe the relationship between the total downtime and the PM interval by technical economic analysis. Secondly, according to the maintenance data of recorded failures and the estimated number of defects identified at PM,the statistical model based on the delay-time maintenance theory is developed to determine the expected number of failures within a PM cycle. The statistical model is tested to be correct by computer simulation test. Therefore,the parameter values of the statistical model,such as the process by which defects arise,of the delay time distribution and the probability of detecting a defect at PM are estimated by the method of maximum likelihood Finally,a case study is given. dentified,which is based upon the estimated model parameters An optimal inspection interval of PM isiand PM model.

Key words: delay time, preventive maintenance(PM), parameter estimation, modelling