Nondispersive infrared absorption spectroscopy(NDIR) is an important method to measure CO concentration in the air. In the present study, an open-path measurement system and continuous measuring device was developed, and genetic programming was used to establish the calibration model of subjects’ light intensity sampling values. Continuous measurements were carried out in 10 different concentration of CO, and 40 sampled data were acquired and analyzed. For validation set, the correlation coefficient was 0.999 7. The biggest relative error of validation was 4.00%, and the average relative error was 1.11%. Results show that genetic programming can be a good method for the modeling of gas concentration measurements equipped with NDIR systems.