The invention discloses a detection device and method for brake force of an elevator traction machine. The device comprises an elevator controller, a traction machine, at least two brakes, an elevator cage, an elevator counterweight, an elevator driving frequency converter and an encoder, wherein the brakes are arranged on the traction machine; the elevator driving frequency converter is connected with the traction machine; the encoder is arranged on the traction machine and can be used for monitoring whether the traction machine rotates; both the elevator driving frequency converter and the encoder are electrically connected with the elevator controller. Whether the brake force of the traction machine reaches the standard can be automatically detected to prevent safety accidents such as slipping caused by insufficient brake force of the traction machine.