For realizing atmospheric alkane gas detection in a wide area and a long distance, a dual-gas simultaneous methane (CH4) and ethane (C2H6) sensor system was demonstrated. Measurements were conducted in an area. A Continuous-Wave (CW) Interband Cascade Laser (ICL) was used as the light source, a high-speed Data Acquisition card (DAQ) was used to acquire the detection signal, and a LabVIEW based laptop platform was developed for signal generation, signal acquisition, harmonic extraction, concentration calculation, and display. Considering sampling period, local wind speed, and vehicle speed, the calculated response time is 82.5 s, and the measurement time is 85-90 s. The noise level of CH4 is ± 40 nL/L and C2H6 is ± 2 nL/L in the laboratory, while CH4 is from +40 to -80 nL/L and C2H6 is ± 4 nL/L in mobile conditions. Furthermore, a good agreement was found between this sensor and a commercial sensor from Aeries, USA. Concentration measurements of CH4 and C2H6 along a street and a 2-D concentration distribution in one block were shown. The varied relationship between these two kinds of gases was analyzed. This work provides a technique for detecting the leakage of alkane gases and monitoring the atmospheric gases.