Abstract: Power transformer is one of the key equipment for the power grid. It is significant to the safe and stable operation of power grid. During the 13th Five-Year Plan period, the investment of distribution network construction will reach 1.7 trillion RMB, which makes a big market for power transformer. In recent years, the manufacturing industry of power transformer in China develops rapidly with high competition. The quality risk of power transformer cannot be ignored. Sampling inspection has become an important means of quality control for power transformers, but due to the diversity of sampling mode strategy, sampling results vary greatly. It is significant to study on optimization of sampling inspection mode and strategy, which can improve the efficiency, quality level, and the reliability of power supply. The research status and theory of sampling inspection are analyzed. The evaluation index system of transformer sampling efficiency is put forward, including the unqualified inspection rate, the qualified rate of the item, the qualified rate of the product, and the sampling efficiency index. At last the evaluation index put forward is verified by the real example.