Abstract: A test vector generation algorithm based on failed vectors information is proposed to solve the low generation efficiency problem for finding hard to detect stuck-at faults in digital circuits. Utilizing the non-correlation properties between the failed and successful test vectors in each port of the primary input, the method increases the generation probability of successful test vectors gradually for hard to detect struck-at fault through the probability information of logical values at primary input of previous failed vectors. By moving away from the test vectors similar in properties to these failed test vectors, the test vector space is vastly reduced.