The invention discloses a sinking device of an open caisson, comprising a precast pile used for supporting an open caisson structure main body. The sinking device of the open caisson is characterized by comprising a bidirectional stress jack and an axial connector, wherein the bidirectional stress jack is tightly and fixedly connected with the open caisson structure main body and positioned between the open caisson structure main body and the precast pile, and the bidirectional stress jack is used for upwards supporting and downwards drawing the open caisson structure main body; and the axialconnector is used for tightly and fixedly connecting the bidirectional stress jack with the precast pile. Because the invention utilizes the bidirectional stress jack tightly and fixedly connected with the open caisson structure main body and the precast pile, the sinking device of the open caisson can be used for supporting the open caisson structure main body in the sinking process of the open caisson and also can be used for drawing the open caisson structure main body. Therefore, the dead weight of the open caisson is reduced, and the controllable, precise and stable sinking of the open caisson is realized; in addition, the invention further discloses a sinking method of the open caisson with the sinking device.