Measuring system and measuring method

A measuring system, comprising:

• a lighting instrument, configured for providing illuminating light, wherein the illuminating light passes through a mask to form initial light;
• an imager, configured for imaging the initial light to form imaging light;
• a beam splitter, configured for splitting the imaging light into projection light and reference light, wherein the projection light is projected to a substrate to form an image of the mask in the substrate, and the substrate is configured for reflecting the projection light to form first reflected light onto the beam splitting unit;
• a reflector, configured for receiving the reference light to form second reflected light, and for projecting the second reflected light onto the beam splitter, the second reflected light and the first reflected light interfering with each other to form interference light;
• and
• a measuring device, configured for measuring an aerial image formed from the interference light, the aerial image formed from the interference light being substantially the same as the image of the mask through which the illuminating light passes.