The invention proposes a distribution network transmission capability calculation method considering operation randomness, which belongs to the field of power system planning and evaluation. The distribution network transmission capability calculation method comprises the steps of: firstly, establishing a distribution network maximum transmission capability calculation model consisting of an objective function and constraint conditions; secondly, transforming the constraint conditions of the model, collecting an active load prediction error value set and a distributed power supply prediction error value set of all nodes in a distribution network at each moment, constructing corresponding probability distribution sets of uncertain quantities according to statistical information, constructing opportunity constraints containing a spinning reserve constraint, and transforming the opportunity constraints into certainty linear constraints by utilizing convex relaxation; and finally, solvingthe model by adopting a convex programming algorithm to obtain the maximum transmission capability of the distribution network. The distribution network transmission capability calculation method constructs the opportunity constraints containing transmission power and transfer capability, can obtain a solvability result, and can be applied to the rapid and efficient evaluation of the transmissioncapability of a large-scale complex power grid in actual production.