A miniaturized passive laser heterodyne detection system is built for monitoring atmospheric environment with a near infrared diode laser operating at 1.57 μm as the local oscillator light source. In order to evaluate the performance of the system, we use light emitted by an external cavity laser with narrow linewidth as the signal light mixing with the local oscillator light. The bandwidth of the system is 0.032 cm -1 and the minimum detectable sensitivity is 25 pW, which is 1/68 of the dark current noise power of photodetector. CO2 solar spectral signal is measured with the system. The volume fractions of two main absorption lines are inverted, and the values are all around 396×10 -6 with measurement error of 7.6×10 -6. The measured results are consistent with the actual CO2 column concentration in the whole atmosphere, and the feasibility of the system for atmospheric environment monitoring is verified.