Tunable diode laser absorption spectroscopy (TDLAS) has a good prospect of application in rapid measurement of trace gases, due to its high resolution and high sensitivity. A real-time measurement system for atmospheric CO and CH4 based on open- path TDLAS is developed, which has a simple structure with direct absorption techniques, avoiding concentration calibration in wavelength modulation techniques. In the system, the data acquisition and processing is performed using a micro controller unit (MCU) of STM32, then the data is sent to DWIN graphical utilized software (DGUS), showing gas concentration and light intensity online, and the curves of gas concentration and light intensity versus time. The concentration and light intensity data is saved in the SD card. This system can replace the upper computer operation to achieve miniaturization. The system combining direct absorption method and a 2333 nm band laser is presented, and is utilized to monitor carbon monoxide and methane at Kexue Island of Hefei with 750 m optical path. The measurement result shows that the atmospheric CO concentration is lower than the CH4 concentration. The system has been tested for a long time to verify its stability, and its detection limit is 0.205 mg/m3 for CO and 0.181 mg/m3 for CH4.