OBJECTIVE：To provide r eference for optimizing the review rules of PASS system and improving rational drug use in our hospital. METHODS ：The prescription review of Calcineurin inhibitor （CNI）was taken as an example. The pharmacists of our hospital collected the inappropriate rules in PASS system in their daily work ，and modified and improved them. Three thousands outpatient prescriptions and inpatient orders containing CNI in the fourth quarter of 2019（before the rule modification ） and the fourth quarter of 2020（after the rule modification ）were randomly selected for our hospital. The warnings ，false positives and false negatives of PASS system review were compared before and after rule modification. RESULTS ：There were some problems in the PASS system of our hospital ，such as too strict judgement on off-label use ，lax review rules ，false positive in the audit of contraindications ，failure to grade warnings according to the severity of drug interactions ，inaccurate judgment of patients ’ liver and kidney function ，lengthy problem description ，incomplete or wrong information in the system database ，lack of effects information of food and traditional Chinese medicine on CNI ，etc. In view of these inappropriate rules ，the pharmacy department of our hospital improved the quality of PASS system review rules through formulating the standardized management process of off-label use ， reasonably enabling the interception function of PASS system ， modifying the false-positive rules of drug contraindications，warning drug interaction by grade ，reviewing in combination with laboratory test reports ，and real-time maintenance of system database information and adding patient education content. The number of warning had decreased from 182 to 105，and the proportion of false-negative and false-positive review results from 25.03％ to 0.43％ after a year of optimization. CONCLUSIONS：The optimization of CNI review rules can enhance the applicability of the PASS system ，facilitate the advance of the prescription pre-review ，and promote clinical rational drug use.