The process capability indices (PCIs) are widely used to evaluate a manufacturer's general process capability. PCIs are generally defined as the ratio of the allowable tolerance of a quality characteristic to the actual process performance. Besides, First Pass Yield (FPY) is also an index to evaluate qualify characteristic progress. However PCIs and FPY are not enough for defining so call ”Guard-band” of some testing items with high/low and room temperature. In order to well control quality cost and have good productivity, manufacturer should have a general rule to evaluate the test items between pre-production and mass production stage. This article is not only to provide a general rule for eliminating/sampling test items, but also a method to facilitating process improvement.