Traditional colorimetric temperature measurement method commonly used in visible and near infrared band, can only get high precisions when measuring near high temperature target, and can′t get high precisions when measuring far low-middle temperature target. Aimed at the limitations of traditional method, infrared colorimetric temperature measurement method was put forward considering atmosphere and ambient radiance, an colorimetric temperature measurement system based on middle infrared camera was established. First, standard blackbody was used for calibration of middle infrared camera and single-band of colorimetric system; then colorimetric temperature measurement model with ambient radiance parameter was deduced, a new function between ratio of two radiances and temperature of target was established; finally, measurement temperature of home-made gray-body in the laboratory was made, the feasibility of proposed method was verified. Experiments show that: in the experimental temperature range, absolute error of temperature measurement is less than 4 ℃, the temperature relative error is less than 6.7%, the measurement accuracy of radiation intensity is higher than 10%. The colorimetric temperature measurement method considering atmosphere and ambient is greatly superior to traditional method.