1. A safety monitoring system for human-machine symbiosis, comprising: a spatial image capturing unit, disposed in a working area, is configured to acquire at least two skeleton images; an image recognition unit is configured to generate at least two spatial gesture images corresponding to the at least two skeleton images, based on information of changes in position of the at least two skeleton images with respect to time; a human-robot-interaction safety monitoring unit is configured to generate a gesture distribution based on the at least two spatial gesture images and a safety distance; and a process monitoring unit is configured to determine whether the gesture distribution meets a safety criterion.