The invention relates to the technical field of flatness detection devices, and proposes a wooden door flatness detection device and a detection method. During the detection process, the requirements for the position and posture of the wooden door are relatively loose, the applicability to the environment is good, the operation is relatively simple, and the detection is more flexible. The device comprises a height adjustment component, a central main body component and a planetary detection component. The central main body component comprises a central guide cylinder, the central guide cylinder is fixedly connected with three angle frames, and the three angle frames are rotatably connected with parallel rods and linkage gears, the three parallel rods are rotatably connected with support rods, the three linkage gears are fixedly connected with linkage rods, the three linkage rods are respectively rotatably connected with the three support rods, and the three support rods are installed with support suction structures. The height adjustment component comprises a triangular frame, the central guide cylinder is provided with a triangular hole, the triangular frame is slidably connected in the triangular hole, three synchronous racks are fixedly connected in the triangular frame, and the three synchronous racks are respectively meshed with the three linkage gears.