LDI focusing system

The invention discloses an LDI focusing system, and relates to the technical field of direct writing exposure, and the LDI focusing system comprises an upper computer, a motion platform, and an alignment camera, an alignment lens cone, a light source and a distance measuring sensor which are arranged on the motion platform. Wherein the top of the alignment lens cone is connected with the alignment camera, the light source is fixed at the bottom of the alignment lens cone, and the distance measuring sensor is fixed on the light source; the motion platform is used for bearing the PCB and driving the PCB to move in the z-axis direction, and the distance measuring sensor is used for detecting the distance of the PCB relative to the motion platform. The upper computer is connected with the motion platform, the alignment camera and the distance measuring sensor, the upper computer judges whether the mark of the current PCB is in the focal plane of the alignment lens cone or not according to data fed back by the dis