The present application provides a prefabricated structural system and an assembly method thereof. The prefabricated structural system may be applied to steel structures, reinforced concrete structures and timber structures. When applied to the steel structures, the prefabricated structural system includes a plurality of steel structure joints and related members. The steel structure joints and related members further comprise: a beam-column connecting sleeve, comprising a first box-shaped steel tube and first C-shaped sleeves extending from and perpendicular to outer surfaces of the first box-shaped steel tube, wherein the first C-shaped sleeve is provided with first wedge shaped recesses at ends of upper and lower flanges thereof; columns, having a column connecting end inserted into the first box-shaped steel tube; main beams, having a main beam connecting end inserted into the first C-shaped sleeve; and main beam fixing steel plates, provided with first wedge shaped protrusions that are tenon-mortise-jointed with first wedge shaped recesses at both sides of the first C-shaped sleeve. In addition to the steel structural construction, the beam-column connecting sleeve of the prefabricated structural system may be further extended to reinforced concrete structures and timber structures.