The principal problem in which infrared thermographic measurements are concerned with is the emissivity of material.Infrared thermographic system was usually used to detect enemy on battlefields.However,landscape engineering is a common camouflage works on battlefields.Thus,according to energy equilibrium law,the leaf emissivity simulate model was set up to estimate the leaf emissivity.Further,the infrared thermographic system was used to analyze the thermography of concrete structure and plant leaf when the environmental temperature difference is within 0.5.The experimental results show that there are approximate linear regression lines between the emissivity parameter of infrared thermographic system vs.the mean temperature of these two targets.But there are obvious different linear regression lines between the emissivity parameter of infrared thermographic system vs.standard error of mean temperature of these two targets.The different characteristic of infrared thermography between concrete structure and plant leaf will promote the detecting ability of infrared thermographic system when the environmental temperature of target area is under the slight temperature difference.