Water coning is easy to appear in heavy oil reservoir with bottom water, which results in earlier water breakthrough and great difficulties to the development of the reservoir. So it is very important to determine the critical production rate of oil well. At present, most of the calculation methods for critical production are established without start-up pressure gradient. A new method for calculation of critical production for heavy oil reservoir is established in this paper, considering start-up pressure gradient. Through instance analysis, it can be seen that this calculation method is more accurate and better meet the actual situation of the field, and has quite important guiding significance.