The invention discloses a method, a device and a system for adjusting light spots received by a light valve and belongs to the field of laser projection. The method includes using a testing device for reflecting the light spots received from a light machine illuminating system to the screen and form a light spot image on the screen, wherein the light spot image comprises part or all of contour line images; adjusting the relative positions of the boundaries of the light spot image and the contour line images until an absolute value of a distance difference of at least one group of calibration distances is not more than a corresponding distance difference threshold value, wherein each group of calibration distances includes the distances between two opposite sides of the light spot image and corresponding sides of the contour line images, the size of the testing device is as same as that of the DMD light valve, the reflection surface of the testing device for light reflection is provided with contour lines, and the contour lines and boundary lines of a display region of the DMD light valve are arranged correspondingly. The method, the device and the system for adjusting the light spots received by the light valve are used for digital light processing projectors and solves the problem of low light spot adjusting precision, so that image display effects are optimized.