Flatness detection device and detection method

The invention discloses a flatness detection device which is used for detecting flatness of an oil seal of a transmission and comprises a detection platform, a dial and a rotator. The rotator is provided with a probe. The detection device is characterized in that the dial comprises a large dial and a small dial; the detection platform and the large dial are an integrated disc; the small dial is disposed above the large dial; and the small dial and the large dial share the same center of a circle. The flatness detection device has a simple structure and high detection precision, and can be used to rapidly and accurately detect flatness of an oil seal of a transmission. A flatness detection method is simple to operate, has small error and can be adopted to effectively solve the oil leakage problem of the oil seal of the transmission.