SEC reserves reflect the development and marketing potential of an oil company. Different from technical recoverable reserves in China, SEC reserves is more easily affected by oil price, operating cost and well performance. Based on qualitative research of other evaluators, this paper analyzed quantitatively the correlation between SEC reserves and its four main influencing factors (oil price, operation cost, initial rate and decline rate) on the basis of calculation results of typical units in Shengli Oil Company and made relative plate. A simple and feasible method to forecast SEC reserves was found herein and proved to be accurate enough by a real evaluation example.