The invention discloses a system and method for testing no load and load of an ultra-high voltage transformer and belongs to the technical field of high voltage tests. The system comprises a test power supply which outputs test voltage and test current to a tested object, a control module which controls the test power supply to generate controllable power supply, outputs an acquisition command tothe data acquisition module, controls system operation, centralized measurement, data processing and safety monitoring, and the data acquisition module which collects test data and the running electrical quantity of each module of the system and transmits the test data and the running electrical quantity to the control module, wherein the test data comprises the test current, the test voltage anda phase difference of the voltage and current. The system can directly measure the no-load loss and load loss of an ultra-high AC voltage transformer and an ultra-high voltage converter transformer onsite. 100% of rated voltage can be applied to the tested transformer in a no-load loss measurement test, and 50% of rated current can be applied to the tested transformer in a load loss measurement test.