The invention discloses a heat dissipation system of an underground box type transformer, comprising a natural convection heat dissipation system mechanism formed by air chutes arranged around a transformer body in a pit box and a ventilation opening arranged on the ground. The heat dissipation system is characterized by further comprising a reinforced heat exchange mechanism which is arranged onat least one outer wall of the transformer body (4) and contacted with the inner wall of the pit box (1), so that the heat generated by the transformer body (4) is transmitted into the pit box (1) through the reinforced heat exchange mechanism, and the heat is then transferred into the surrounding stratum through the pit box. The heat dissipation system combines natural ventilation and forced ventilation, and adopts surface soil layer heat dissipation, so as to improve the heat dissipation effect and ensure lasting and stable heat dissipation; furthermore, the size of the pit box can be reduced to the utmost extent, and the pre-buried underground space is saved.