The invention discloses a synchronous gearless traction machine braking force detection device. The device comprises a torque bar, a weight tray and a testing weight, wherein the torque bar is detachably mounted on a traction wheel of a synchronous gearless traction machine, and the torque bar is located at a counterweight side of the traction wheel and is arranged horizontally, the torque bar protrudes to the outside of the traction wheel, the weight tray is hung on one end far away from the torque bar, the test weight is selectively loaded in the weight tray, if the test weight loaded in theweight tray makes the selectively deviate from an initial horizontal position, a braking force of the synchronous gearless traction machine is not enough, and if the torque bar maintains the initialhorizontal position under the function of the test weight, the braking force of the synchronous gearless traction machine is qualified, thus, whether the braking force of the synchronous gearless traction machine is qualified can be visually judged through observation for the position of the torque bar, the device is easy to understand, a detection method is simple, generates an accurate result and can perform quantitative analysis. The invention also discloses a synchronous gearless traction machine braking force detection method.