A double grating displacement measurement system with the resolution of nanometer order is analyzed theoretically. A mathematic model of the double grating displacement measurement is established. An ultra-precision positioning set based on laser Moiré signals is designed, which achieves high-accuracy position detection and full automatic precision plane alignment. In view of the existing non-linearity and the difficulty in establishing precision controlled model, fuzzy control method is used in the precision positioning control. The bach propagation(BP) neural network is used to set up a fuzzy neural network controller (FNNC) model. Driving signal is obtained by mapping Moiré signals′ intensities and their intensity rates. The improved fuzzy control system can obtain corresponding operation knowledge according to working environment. The experimental result shows that FNNC can perform excellent control effect such as good stability and strong robustness, and that the positioning speed and positioning accuracy can be effectively improved. The device based on fuzzy neural network can achieve positioning accuracy of ±0.4 μm.