In order to improve the high temperature permeability， anti-metal permeability and thermoplasticity of water-based coating for precision molding， the coating is modified by introducing high temperature fading agent， thermoplastic particles and low-expansion materials. With coating layer thickness and permeability as the output index， orthogonal test is designed to investigate the optimal addition of raw materials. The results show that the permeability at high temperature and the anti-sand properties of the coating can be improved by introducing suitable thermoplastic particles， high temperature fading agent and materials to reduce the thermal expansion rate. On this basis， the water-based coating of sand mold used for precise shaping process with good coating performance and permeability was obtained by taking the coating layer thickness and penetration depth of the coating as the experimental output index and optimizing the addition amount of aggregate， graphite， wetting agent and surfactant.