Abstract:  Aiming at the problems of three phase transformers voltage ratio and connection group code test, such as more connecting wires, complex test process and the test result not being audiovisual, a micro computer based measurement, data processing and control system was successfully developed. This device only employing single phase power supply can at the same time automatically measure the voltage ratio and connection group and the test result can directly be displayed in digital. In the voltage ratio circuit design, the principle of two voltage meter method is adopted, a high precision A/D transformer is used and a microcomputer is employed to measure voltage and calculate the voltage ratio values. In the connection group code circuit design, the principle of phasemeter method is employed, i.e. adding a threephase A.C. voltage on the primary coil to detect the phase difference between primary and second coils, and thus the value of connectiongroup code may be judged. Experimental test shows that this system possesses the advantatges of good antidisturbed ability, high test precision and easy operation.