As one of the greenhouse gases, ethane can promote the generation of photochemical pollution and destruction of ozone. Due to its extremely low concentration in the atmosphere, it requires a sensor with high accuracy for measurement. A continuous-wave interband cascade laser (ICL) based on mid-infrared sensor system with high-precision of 10-9 level is demonstrated for detection of ethane in atmospheric. A multi-pass gas cell with volume of 220 mL and an optical path of 54.6 m is used. The LabVIEW visual instrument platform is used to program the scan and modulation signal as well as their superposition. A date acquisition (DAQ) card is employed to output the signal of the ICL driver. The output signal from detector is acquired by the DAQ and programmed by LabVIEW for data processing such as lock-in amplifier and second-harmonic extraction. Experimental results show that an Allan deviation of 1.86×10-9 for ethane with an averaging time of 1.67 s is achieved, and it is as low as 0.026×10-9 at an averaging time of 775 s. Outdoor atmospheric ethane concentration measurement is carried out in a compressed natural gas station. The experimental result shows that this ethane sensor system has a great practical value in application.