The invention provides a heavy box type building module, a heavy box type modular building and a construction method of the heavy box type modular building. The heavy box type building module comprises a frame box formed by welding two top longitudinal beams, two top cross beams, two bottom longitudinal beams, two bottom cross beams and four supporting columns. The frame box is reasonably provided with door and window keels, bearing keels, window frame keels, roof keels, building surface keels and slant supports. The heavy box type building module is high in integrity and stability. The heavy box type modular building is formed by multiple stacked heavy box type building modules, and every two adjacent heavy box type building modules are connected through bolts. The heavy box type modular building is short in site construction period and fewer in labor demands and influences on the environment. The invention further provides a construction method of the heavy box type modular building.