The invention relates to the field of material surface magnetism measurement, and discloses an in-situ measurement method for sample magnetism. The in-situ measurement method adopts a measuring device, wherein the measuring device comprises a light source, an aspherical mirror I, an aspherical mirror II, a field diaphragm, a polarizer, an aspherical mirror III, a translucent reflector, an objective lens, a laser device, a sample, a sample platform, a substrate, a stepping motor, an inclined plane bench, an ejection pin, a magnet, slit diaphragms, a photoelectric detector I, a compensator, ananalyzer, an aspherical mirror IV and a photoelectric detector II. According to the in-situ measurement method, the illumination region on the sample does not need to be changed by means of the diaphragm slits, the Kerr sensitivity in different directions is measured, the mechanical instability in the experiment is reduced, incident light intensity in different directions are adjusted through adjusting the number and the duration of turned-on LED lamps, the intensity of incident light is adjusted in real time according to the acquired image quality so as to obtain an image with good resolution, and especially for some magnetic samples with complicated magnetization directions of magnetic domains, the magnetoelastic property of the sample can be studied in situ through adopting the method of applying stress to the back surface of the sample.