The invention relates to an in-mould coating method and a device thereof. The core of a shaping die emitted out by the in-mould coating device is a transparent material and the outer surface of a shaping product of the core is coated with a layer of reflective material layer; a beam generator, a beam sensor, a vidicon,etc. are arranged in the core; the coating method is that after a semi-finishedproduct shaped by being emitted or by other technical methods is placed into a mould and then matched moulds are closed, liquid paint vehicle or other liquid materials coated are injected in a clearance which is designed and generated between the transparent core and the semi-finished product, and the vidicon is used for monitoring filling situation; after the filing is finished, the beam generator arranged in the transparent core is started and the beam sensor is used for monitoring the beam irradiation amount of the liquid paint vehicle or other liquid materials coated which are injected into the mould, so that after the chemical change solidification is generated, a film coated is formed, and the film coated is coated and bonded on the surface of the semi-finished product, namely leading the semi-finished product shaped by being emitted or by other technical methods to obtain the needed appearance or function of a finished product.