In order to reduce the second rescue injuries and deaths after the mashgas exploding in the mine, a portable imaging interferometer system is designed to detect CO temperature and concentration by the passive and remote measurement. The CO temperature and concentration are detected according to the rotational spectral line of CO gas molecule and the linear relationship between the radiation intensity of gas molecule and the molecule number density, respectively. The optical system is designed, and then its forward is studied in this work. The forward expression is obtained after studying the following four seed models of the optical system: the radiation model of target gas, where CO six emission spectral lines R11-16 are selected from HITRAN08 database; the mine CO gas transmission model in which the absorptions by the water vapor and CO2 molecule, and absorption and scattering by the mine aerosol are calculated by the relevant rules; the filter function model, in which the matched parameters of the band width of 0.5 nm and max transmittance of 0.23 for CO temperature are measured by the method of rotational line of R11-16, and the model of imaging detector CCD in which the infrared CCD of pixel 320320 and the max quantum efficiency of 0.75 are to be used in the optical system. According to the given parameters and MATLAB programming, the forward imaging interference results of CO differentiable six spectrum of R11-16 are obtained. The forward max noise-signal ratio is 268 when the exposure time is 300 s. The max electric count is 1.5105 that is larger than the selected CCD dark noise of 400 e but less than the CCD full charge quantity of 1106 e. The forward result clearly indicates that the optical system can meet the initial design demand. The accuracies of CO temperature and concentration measured by this optical system can reach 2 K and 0.1%, respectively. This portable system can be used to detect not only the mine CO, but also other gases like the pipe smoke, bomb exploding gas, etc. in which the filter and CCD need to be changed.