Accounting reduction of crude oil production capacity as a significant part in determining crude oil production capacity determines the rationality of reduction work. To avoid such two cases of more reduction in old mining area when actuality is better than planned and of less reduction when actuality is lower than planned, this paper uses ARPS model to establish a theoretical model of accounting reduction rate of crude oil production capacity and reduction reliability, which is used to draw a plot that can be referred to determine the rationality of accounting reduction in different oilfields or developing units. There is a theoretical connection between accounting reduction rate of crude oil production capacity and comprehensive declining rate and accounting reduction rate should be, not related to natural declining rate, bigger than comprehensive declining rate. The reliability of accounting reduction of crude oil production capacity is 1.7-1.8 if annually comprehensive declining rate is less than 20%. A case study on east zone of Wangji Oilfield, Henan province proves the rationality of crude oil production capacity indexes and accounting reduction rate in this block.