Provided is a frequency-conversion voltage-regulation on-site no-load test method for a large extra-high voltage transformer. An alternating-current test power source, an intermediate transformer and the tested transformer are connected in sequence, one or more sets of high-voltage filters are connected with a primary portion of the tested transformer in parallel, the high-voltage filters are connected with higher-harmonic RLC in series, a high-voltage high-power variable-frequency power source or the output end of the high-voltage high-power variable-frequency power source is connected with a voltage regulator to serve as the alternating-current test power source, and a no-load test is carried out on the tested transformer through frequency regulation operation on the high-voltage high-power alternating-current test power source to achieve carrying out the no-load test of the large transformer on the premises that the capacity of the no-load test power source is not increased, the quality of a no-load voltage waveform is not degraded, and the capacity of the high-voltage filters which are used for carrying out compensation is not changed. According to the frequency-conversion voltage-regulation on-site no-load test method for the large extra-high voltage transformer, the capacity of the test power source needed by the large extra-high voltage transformer is remarkably reduced on the premise that the boosting process is smoothly accomplished, and therefore an extra-high voltage transformer on-site test technology and device are effectively promoted to achieve integration, miniaturization and site practicability.