Employing a test platform in an SOC design has been shown to be an effective method for SOC testing. However the test efficiency problem of a test platform has not been addressed. In this paper, we formally analyze the test efficiency of test platforms and seek for its optimization. We formulate the required numbers of test cycles for test platforms implemented with different test structures and/or executed with different test procedures. It is shown that up to 24X test time difference for platforms with different test structures/procedures is possible. Based on the derived formula, an appropriate test platform that can achieve best test efficiency with minimal area overhead can be determined.