A head mounted displaying system and an image generating method thereof are provided. The head mounted displaying system includes a displaying device, a movement sensor, a frame, an image generating system and a physiological information sensor. The movement sensor senses a movement of an object or senses a movement of the displaying device. The frame is configured to fix the displaying device. The image generating system is coupled to the displaying device. The image generating system displays an image through the displaying device. The image includes a first part. The first part is irrelative to a sensing result of the movement sensor. The physiological information sensor is disposed at the frame and coupled to the image generating system. The image generating system adjusts the first part of the image displayed by the displaying device according to physiological information sensed by the physiological information sensor.
