The invention provides a laser pen which comprises a pen body, a power supply switch, a laser generator, a pen head fixed to one end of the pen body and a measuring device contained in the pen head. The measuring device comprises a dial and a measuring disk; the peripheral wall of the dial is provided with scale regions corresponding to the product defect sizes and exposed out of the pen head; the measuring disk is provided with a plurality of round holes which correspond to the scale regions of the dial and are used for transmitting laser beams generated by the laser generator; and the dial is fixedly connected with the measuring disk and can be rotated to adjust the sizes of the round holes of the measuring disk on a light path of the laser generator so as to control the size of a lightspot generated by the laser pen.