The invention discloses a design method for a middle connector stress cone of a high-voltage alternating-current cable. The method comprises the following steps that S1, mathematical model software isadopted for establishing a mode of a prefabricated connector which is connected with the cable; S2, the diameter expansion distance x of the prefabricated connector in the model is changed continuously, accordingly, a series of the end height h and end length l of the corresponding strain cone are obtained, and the tangency angle alpha between the root of the strain cone corresponding to each diameter expansion distance x and the inner surface of the prefabricated connector is calculated; S3, linear fitting is conducted by adopting the least square method, and the functional relation betweenthe end height h of the strain cone and the diameter expansion distance x, the functional relation between the end length l of the strain cone and the diameter expansion distance x and the functionalrelation between the tangency angle alpha of the root of the strain cone and the inner surface of the prefabricated connector and the diameter expansion distance x are obtained respectively; S4, the actually required diameter expansion distance x is introduced into all the functional relations, and the end height h of the strain cone, the end length l of the strain cone and the tangency angle alpha between the root of the strain cone and the inner surface of the prefabricated connector which are actually required are obtained.