The invention provides a limited slip differential assembly and a main speed reducer. The limited slip differential assembly comprises a spiral bevel gear, a left planetary gear, a right planetary gear, a left half axle gear, a right half axle gear, a first friction mechanism and a second friction mechanism, wherein the spiral bevel gear is connected with a right differential end cover, the right differential end cover is connected with a differential housing, and the differential housing is also connected with a left differential end cover; the left planetary gear is installed in the left differential end cover; the right planetary gear is installed in the right differential end cover; the left half axle gear is installed in a first gear mounting hole in one end of the differential housing; the right half axle gear is installed in a second gear mounting hole in the other end of the differential housing; the first friction mechanism is installed between the left differential end cover and the differential housing; and the second friction mechanism is installed between the right differential end cover and the differential housing.