The invention belongs to the field of gearboxes, and particularly relates to an automatic gearbox of an automobile. The automatic gearbox comprises an A gear column body, a B gear column body and a reverse gear system body, a power input shaft and a power output shaft are arranged on the A gear column body, the power input shaft is connected with the output end of an engine rotating clockwise, a first driving gear, a second driving gear, a third driving gear and a fourth driving gear are arranged in the A gear column body, a first ratchet, a second ratchet and a third ratchet which are clockwise in one direction and sequentially inserted in the first driving gear, the second driving gear, the third driving gear and the fourth driving gear are further arranged in the A gear column body, the overall structure of the A gear column body is that the first driving gear and the first ratchet are integrated, the first ratchet is connected with the second driving gear, and the second driving gear and the second ratchet are integrated. According to the automatic gearbox, the service life of the gearbox is prolonged, the power loss is relatively small, and the balanced power demand can make the engine no longer powerless.