Flatness measuring device and using method thereof

The invention relates to a flatness measuring device and a using method thereof. The flatness measuring device comprises a main ruler and a laser range finder, wherein a horizontal bubble is arrangedon the top face of the main ruler, a telescopic adjusting piece is arranged on the bottom face of the main ruler, the length of the adjusting piece is correspondingly adjusted according to the horizontal bubble, and the main ruler is made to be horizontal; the laser range finder is mounted on the top surface of the main ruler and can be moved and adjusted in the length direction of the main ruler,the laser range finder is moved along the main ruler and emits laser to a to-be-measured structure to measure the distance between a multiple sets of main rulers and the to-be-measured structure, andtherefore the flatness of the to-be-measured structure is obtained through comparison. Thus, the problem that the flatness of the to-be-measured structure is difficult to measure is effectively solved, the measurement precisio