The invention relates to a tunnel construction microseismic monitoring system and a monitoring method. The method comprises the steps that sensors are used to collect seismic source information; a number of sensors are spatially and three-dimensionally distributed inside and outside a tunnel and are connected with a collector; according to the waveform of the seismic source information, rock massfracture seismic source information and auxiliary seismic source information are separated; real-time data processing is carried out on the acquired seismic source information to acquire an effectivedata processing result, including the location, time and energy of cracks generated by a microseismic event corresponding to the rock mass fracture seismic source information and the corresponding shock wave transmission speed; according to the data processing result of the rock mass fracture seismic source information, rock mass cracks are located; and the energy and time of the microseismic event corresponding to each located rock mass crack are combined to acquire the time distribution law and the spatial distribution law of the cracks generated by the rock mass microseismic event. According to the invention, the location and time of the cracks generated by the microseismic event are accurately described to realize the description of a tunnel rock mass destruction process.