In order to simplify the problem of distribution network planning, the acceptable error and computable problems in distribution network planning are studied after analyzing the uncertainties in the process of distribution network planning. By introducing the acceptable error, the distribution network planning problem is transformed into a computable problem, and the standard mathematical model and algorithm formula of the distribution network planning decision are established. The mathematical model and algorithm are used to calculate the power supply radius of 66 kV substation. Calculation results show that the distribution network planning model and algorithm based on acceptable error are effective and practical. The model and algorithm can simplify the process of distribution network planning and provide reference for determining the principle of distribution network planning. This work is supported by National Natural Science Foundation of China (No. 51377161).