Abstract: Environmental quality in layer houses has been one of the most important influencing factors on the health level and production performance of laying hens in the large-scale poultry industry. This study aims to explore the impact of environmental quality of layer houses on the production performance of laying hens in summer. An analytical method was also proposed using multivariate data fusion. Firstly, seven environmental factors were detected, including temperature, relative humidity, wind speed, light, and concentration of CO₂, NH₃, and PM_2.5, according to the thermal, light, and gas environment. Then, the membership function was used to determine the basic probability distribution function of each factor. The correlation coefficient matrix was also utilized to optimize the support and correlation matrix of environmental factors. After that, the environmental factors were weighted and normalized to obtain the credibility matrix and evidence weights. The basic probability distribution functions were achieved in the thermal, light, and gas environment groups. Finally, the improved D-S evidence theory was used to fuse and iterate the basic probability allocation functions of the three groups, in order to evaluate the environmental quality at each detection point of layer house. A comparison was then made to reveal the impact of environmental quality of layer houses on the production performance of laying hens. A validation experiment was conducted in a layer house with eight tiers of battery cages in summer. The experimental results indicated that the best location was achieved in the front on the lower four tiers of the layer house, in terms of the environmental quality and average laying rate. The worst location for average laying rate was in the middle of the layer house with the comprehensive evaluation of environmental quality normal. The best location for the average laying rate on the upper four tiers was in the middle with the comprehensive evaluation of environmental quality suitable, whereas, the location with the worst average laying rate and environmental quality was at the back of layer house. The most suitable one was found in the comprehensive evaluation of environmental quality at detection points with an average laying rate higher than 86%. While the normal was observed lower than 86%. Once the comprehensive evaluation of the environmental quality was suitable, the average laying rate was relatively higher. On the contrary, the average laying rate was lower with the normal comprehensive evaluation of environmental quality. Furthermore, the improved D-S evidence theory can be expected to accurately evaluate the environmental quality, whereas, the D-S evidence theory cannot, particularly when environmental evidence conflicts with each other. The findings can provide an effective way to accurately evaluate the environmental quality of layer houses in summer, in order to clarify the impact of environmental quality of layer houses on the production performance of laying hens.