In this paper, a vector-less simple technique based on the oscillation-test strategy (OTS) is proposed for the test of the Buck regulator. In the test mode, the circuit under test (CUT) of the buck regulator could be easily transformed into an oscillator for generating the oscillating signal. By observing the frequency and amplitude of the oscillating signal, we could detect the CUT to see if it is faulty or fault-free. Simulation results show that the fault coverage for hard faults could reach up to 99%. Based on the facts of the simple structure and high fault coverage, OTS is considered as a useful technique in the testing of the Buck regulator.