1. A size measuring and comparing system, wherein the system is applied on an electronic device and the electronic device comprises a positioning unit for positioning an object which has a plurality of sides and obtaining a coordinate of each point of the object, the system comprising: a point acquiring module to acquire coordinates of at least four points which are not assigned on a same side of the object from the positioning unit; a model creating module to create a cuboid model including the at least four points as vertices based on the coordinates of the at least four points; a space measuring module to calculate a height and a width of a space; a determination module to determine whether it is feasible for the object to pass through the space based on a length, a width, and a height of the cuboid model and the height and the width of the space; and an output control module to output a result; wherein the modules of the size measuring and comparing system are executable by at least one processor.