Abstract: A test system for testing a device under test (DUT) and a test method thereof. At first, an expected test pattern having a test input signal and an expected output signal is output. Next, the expected test pattern is compressed, and an expected compressed pattern having an expected compressed output signal corresponding to the expected output signal is output and saved. Then, the expected compressed pattern is decompressed, and the test input signal is applied to the DUT for testing the DUT. Next, a real output signal output from the DUT is received and compressed, and then a real compressed output signal is output and saved. At last, the real compressed output signal and the expected compressed output signal are compared to determine the test result.