A novel full optical path laser methane sensor probe has been developed for continuous, safe, and accurate in-situ monitoring of mine gas (methane) concentration. The methane probe, with a volume of only φ4 cm×8 cm (cylindrical), is housed in a stainless steel casing to ensure measurement safety. Internally, the probe consists of all optical components without any related electrical structures, utilizing a three-mirror reflection system to form the optical path. The absorption path of the probe is approximately 20 cm. The methane probe is characterized by its high sensitivity, strong robustness, and high safety. To validate its performance, a methane concentration detection system based on laser probes was constructed in the laboratory, using a distributed feedback laser (DFB) with a central wavelength of 1 653.7 nm as the light source. The system combined wavelength modulation spectroscopy (WMS) and direct absorption spectroscopy (DAS) technologies to achieve high-sensitivity detection of methane gas. Experimental results demonstrate that, at room temperature and pressure, the measurement error is less than ±5.0×10-4 for low concentrations (0~1%), and less than ±5% of the true value for high concentrations, with a full-range linear fitting coefficient of 0.999 8. The detection limit of the sensor (1σ standard) is 68 ppm and the response time is not exceeding 10 s. Experiments confirmed that different distances (1 km、2 km、5 km) from the probe have almost no effect on methane concentration measurements. These results confirm the probe′s capability for accurate methane detection and its suitability for in-situ mine gas monitoring.