Abstract: Based on analysis and improvement of simple response method(SRM) and Weibull reliability method for calibration intervals of test system,and by taking into account fault decisions on the calibration process,the decision risks on verification of test system were resolved.In this paper,related national measurement standards on reliability index of test system were firstly introduced,then some usual calibration interval determination methods were also discussed,and furthermore the reliability probability functions for observational value of test reliability were given.By synthesizing different parameters with principal component analysis(PCA) method,the estimation values of the optimal calibration interval were corrected.Lastly,the results of verification on digital multimeter(DMM) measurement channel in automatic test system(ATS) show that the calibration intervals optimization methods are feasible.