The invention relates to a convex-difference-planning-based calculation method of the maximum access capability of a distributed power supply in a distribution network. The method comprises: distribution network structure and parameter information is inputted, and a calculation accuracy value, an initial penalty coefficient and an iteration number of times are set; according to the distribution network structure and parameter information, a distributed power supply maximum access capability calculation model is established by considering the access capability maximization of the distributed power supply in the system; for nonlinear constraints in the maximum access capacity calculation model, conversion into a second-order cone programming model is carried out by linearization and second-order cone relaxation, and the model is solved to obtain an initial solution to the distributed power supply maximum access capability calculation model; a convex difference inequation is introduced into the second-order cone programming model and linearization is carried out, an objective function is updated; a penalty item is added into the objective function, and conversion to a convex difference programming model is carried out; the convex difference programming model is solved and whether a convergence condition is satisfied is determined; an iterative penalty factor is updated and solution calculation is carried out again; and a result is outputted. According to the invention, the calculation speed is increased substantially; and the maximum access plan of the distributed power supplyis obtained quickly.