In order to solve the problems of huge equipment, workload and security risks in 750kV Transformer error onsite testing, this paper introduces a new design of 750 kV transformer calibration cart for field test. It uses series resonant boost and comparison method to complete the test, and the most distinctive features of the design is the series standard voltage transformers (SSTV). SSTV based on the theory of voltage summation method and parted type structures, it can be divided into two stages and be connected by high voltage isolation transformers (HVIT). This method can greatly reduce the equipment volume and insulation requirements on the premise of meeting the requirements of accuracy and the compressive strength significantly, the bottom is independently used in 330 kV voltage level test and greatly improve the utilization of the equipment. In addition, we introduce the capacitive standard method and the error analysis of the environmental impact of the SSTV. The final practical application example compares the results between the capacitive standard and SSTV, it shows that two results are basically identical, so the transformer calibration cart has the value of practical application.