For the modern painting line, it can generally meet the requirements of constant temperature, constant humidity and clean air (air dust content < 10mg/m3); but for the simpler production line, it is difficult to guarantee constant temperature, constant humidity and clean air, so that the painting workpiece can not achieve satisfactory painting effect, and the film can easily produce pinhole (shrinkage). In order to avoid pinholes and orange peel, the temperature and humidity in the spraying room should be improved to meet the technological requirements. Secondly, the viscosity and diluent composition of the coating should be adjusted according to different temperature and humidity. Generally, it is necessary in the spraying process. The temperature and humidity of the spraying chamber are controlled below 35 C and 80% respectively.