Population of the rare and endangered species Ammopiptanthus mongolicus(Maxim.) Cheng f. declined rapidly in China’s arid region and Central Asia. There is an urgent need to protect this species, which is particularly important in maintaining biodiversity throughout the arid region of northwestern China. By analyzing the infrared thermal images based on plant-transpiration transfer coefficient(h_at) and photosynthetic parameters, we made quantitative and accurate diagnoses of the plant growth and health status of A. mongolicus. Using an LI-COR6400 photosynthesis system, we measured the net photosynthetic rate(P_n), stomatal conductance(G_s), and transpiration rate(T_r). Infrared thermal images obtained in the field were processed by ENVI4.8 software to calculate surface temperatures of the plant subjects. We found that the plant transpiration transfer coefficient of A. mongolicus was in the order of old plants [young plants [intermediate-aged plants. Declining health levels of young, intermediate, and old plants were divided into three categories:0.4, 0.4–0.7,and [0.7. The coefficient showed a significant negative correlation with T_r, G_s, and P_n, indicating that they can simultaneously reflect the state of plant growth. By establishing h_at and photosynthetic parameters in regression model Y = a-blnx, we can accurately diagnose plant growth and decline of plant health conditions. There is an urgent need to protect this species, which is particularly important in maintaining biological throughout the arid region of northwestern China . By analyzing the infrared thermal images based on plant-transpiration transfer coefficient (h_at) and photosynthetic parameters, we made quantitative and accurate diagnoses of the plant growth and health status of A. mongolicus. Using an LI-COR6400 photosynthesis system, we measured the We found that the plant transpiration transfer (G_s), and transpiration rate (T_r). Infrared thermal images obtained in the field were processed by ENVI4.8 software to calculate surface temperatures of the plant subjects. We found that the plant transpiration transfer coefficient of A. mongolicus was in the order of old plants [young plants [intermediate-aged plants. Declining health levels of young, i ntermediate, and old plants were divided into three categories: 0.4, 0.4-0.7, and [0.7. The coefficient showed a significant negative correlation with T_r, G_s, and P_n, indicating that they can now reflect the state of plant growth. By establishing h_at and photosynthetic parameters in regression model Y = a-blnx, we can accurately diagnose plant growth and decline of plant health conditions.