The invention provides a sleeping monitoring system. The sleeping monitoring system comprises a motion sensor, a monitoring device and an output device, wherein the motion sensor is connected with the monitoring device, and an output signal of the monitoring device is connected with the output device. A method of sleeping monitoring comprises the steps of A, presetting the threshold value of a triaxial gravitational acceleration sensor and a reference value during the change of a sleeping posture; B, performing monitoring on human body sleeping, and recording, analyzing and processing real-time accelerated speeds of the change of the sleeping posture and other motion conditions; C, outputting sleeping state information to the output device according to the real-time accelerated speeds of the change state of the sleeping posture and the other motion conditions. The sleeping monitoring system provides beneficial data support for improving the sleeping quality and preventing the unforeseen circumstance that diseases are caused by unhealthy sleeping habits. When a human body is at a light sleep state, an awakening signal is output to an awaking device. The method of the sleeping monitoring adopts the triaxial gravitational acceleration sensor to sense the sleeping posture and the change of the sleeping posture, the cost is low, and the operation is easy.