The invention relates to a civil engineering temporary works design optimization method and a device based on three-dimensional laser scanning. The method comprises steps: the position of a station is determined; at the station position, a three-dimensional laser scanner is used for all-orientation scanning on a target area to acquire three-dimensional data, and the three-dimensional data are used to form a point cloud; the point cloud is used for acquiring a three-dimensional map for the original landform of the target area; according to parameter information of a target works, a building model is formed on the three-dimensional map for the original landform of the target area; on the three-dimensional map with the building model, a civil engineering temporary works is designed; and collision recheck is carried out on the civil engineering temporary works and the building model, and the civil engineering temporary works is optimally designed according to the recheck result.