Aiming at the problem of insufficient positioning accuracy of precision positioning platforms with large travel distances, a novel nanometer accuracy positioning system based on feedback of heterodyne laser interferometry with non-coaxial beams is proposed. The system consists of a composite feedback of heterodyne laser interferometry with non-coaxial beams and high-precision grating scale, which retains the advantages of high-resolution and large travel distance of high-precision grating scale, and combines with heterodyne laser interferometry with non-coaxial beams to form collaborative positioning which eliminates the influence of installation errors and deformation of grating scale on positioning accuracy, and improves the positioning accuracy under large travel distances. The system adopts predictive fine-tuning positioning technology based on BP neural network, which to some extent improves positioning efficiency. The experimental results show that within the travel range of 100mm, the system’s axis bi-directional positioning accuracy can reach 28nm and its axis repeated positioning accuracy can reach 26nm. Through predictive positioning, when the positioning end threshold is set to 20nm, the system’s positioning fine-tuning time can be shortened from within 1.65s to within 0.6s. At the speed of 5mm/s, the tracking error of the system can reach 100nm.