The traditional optical interference measurement method is relative detection method, and the detection accuracy is generally limited by the accuracy of the reference surface shape. The use of absolute detection technology can eliminate the constraint of the reference surface shape error on the interference measurement accuracy, which can realize the measurement of the surface shape in nanoscale. Firstly, N bit rotation average absolute detection method and oblique incidence absolute detection method are introduced. Then the theoretical derivation and simulation analysis of two detection methods and three algorithms (rotation average algorithm, iteration algorithm, odd even function algorithm) used in the process of surface restoration are carried out. Finally, the recovered surface shape accuracy and feasibility of the three methods are verified by the experiments. The advantage, disadvantage and applicability of each method are analyzed and compared. At last, the absolute surface measurement of mirror with aperture of 100 mm for high precision interferometer standard flat with peak valley (PV) value of nearly λ/40 is achieved.