The invention belongs to the technical field of geological prospecting and discloses a methane concentration detecting instrument for coal bed methane drilling. The methane concentration detecting instrument comprises a gauging nipple and a data collecting and storing system located i the gauging nipple. The data collecting system comprises a methane sensor, a data processing chip and a data storage module. The methane sensor is fixed to the gauging nipple and connected with the data storage module through the data processing chip. The gauging nipple comprises a spindle, a battery cabin, a circuit box and a sensor seat. A hole slot is formed in the spindle. The battery cabin is fixed in the hole slot. The circuit box is fixed in the hole slot. The data processing chip and the data storage module are arranged in the circuit box and connected with the battery cabin. The sensor seat is fixed in the hole slot. The methane sensor is fixed to the sensor seat and connected with the data processing chip. The methane concentration detecting instrument for coal bed methane drilling is high in reliability and stability.