The invention belongs to the laser precision detection technology and laser micro-nano processing monitoring technology field and relates to a laser micro-nano processing light splitting pupil differential confocal online monitoring integration method and device which can be used for the laser micro-nano processing and online detection of a complex fine structure. In the invention, a long workingdistance and high axial resolution light splitting pupil laser differential confocal axial monitoring module is organically integrated with a femtosecond laser processing system. A light splitting pupil differential confocal system curve zero point is used to carry out nanoscale monitoring on the axial position of a sample so as to realize the real-time fixed focus of the axial position of the sample and the high precision measurement of a processed micro-nano structure size. A drift problem and a high-precision online detection problem in a measurement process are solved, and the controllability of micro-nano femtosecond laser processing precision, the processing quality of the sample and the like are improved. Before processing, a microscopic imaging module can be used to carry out coarse alignment and transverse position identification on the sample.