The invention discloses a power distribution box and an assembly method thereof. A rotating shaft is arranged between side plates at two sides in a box body in a penetrating manner; rotating shaft mating holes are formed in two sides of a front panel and are in fit connection with the rotating shaft; a first bracket is fixed on the front panel and comprises a first lower plate, an upper plate and a second lower plate; one end of a switch shaft is fixedly connected with a switch handle, an outer disc is arranged in the middle and a fixed plate groove is formed in the other end; a first spring sheet groove and a second spring sheet groove are formed in two sides of the switch shaft; a first stabilizer blade and a second stabilizer blade are arranged at two sides of a spring sheet and are matched with the first spring sheet groove and the second spring sheet groove respectively; the other end of the switch shaft is sequentially inserted into a second switch opening and a first switch opening and then fixed through the spring sheet; and the switch handle drives a switch blade when a door is closed, and then the switch blade is clamped at the rear part of a baffle plate. The power distribution box is reasonable in structural design, stable and reliable in connection, high in universality and convenient to install and maintain, and is suitable for being widely applied to power distribution boxes.