The invention provides a mask pre-alignment system used in a lithography machine. The disclosed mask pre-alignment system used in the lithography machine comprises a first mark and a second mark arranged on a mask table; a first optical path system which comprises a first lighting module, a first imaging module and a first detection module; and a second optical path system which comprises a second lighting module, a second imaging module and a second detection module; the first lighting module comprises a first light source unit and a first collimation unit, and the second lighting module comprises a second light source unit and a second collimation unit, wherein, the first optical path system has the same structure as the second optical path system. The pre-alignment system is characterized by high alignment precision and wide measurement range, can realize the pre-alignment of a mask and a mask clamp with an objective lens workpiece table, causes the mask to enter the capture range of a precision alignment system, thus improving the precision alignment efficiency and causing the mask to be arranged in the scanning range of the objective lens.