This thesis aims at an in-depth research of the phenomenon-steadiness in product quality but low index of work procedure ability, which generally exists in such fields as chemical industry. The research proves that the above-mentioned problem results form the fact that the quality index of work procedure products X is not subordinate to the normal distribution in parts of an area. And it further proves that the current calculating method of work procedure ability index is unadaptable in some areas such as chemical industry. According to the research result of the thesis, it can be concluded that redefining the calculating formula of work procedure ability index may lead to an effective solution of the above problem, with the quality index of work procedure products X subordinate to the above abnormal distribution, mathematical statistics as fundamental principle, and the probability leading to the first-class error less than 0.27%.