The utility model belongs to the technical field of elevators, and particularly discloses a gravity type vertical elevator for a double-layer building, which comprises a layer plate, a car with a variable accommodating space, a pulley block, a transmission strip and a control system for controlling the elevator to lift. According to the utility model, the traditional counterweight block is replaced by the lift car; the characteristic that the size of the car accommodating space is variable is utilized; the gravity difference exists between the double cars on the upper layer and the lower layer; utilizing lever principle, the heavy upper-layer lift car transports people flow to the lower layer while the lower-layer lift car transports people flow to the upper layer, two-way people flow transportation is achieved, the problems that in the prior art, an elevator is complex in equipment system, large in traction power, large in structure energy consumption, difficult to maintain and repairand the like are solved, and the hole utilization rate of an elevator and the transportation speed of a double-layer elevator are greatly increased.