A physiological signal measuring method includes a training's thermal image providing step, a training step, a classification model generating step, a measurement's thermal image providing step, a mask-wearing classifying step, a block identifying step and a measurement result generating step. The measurement's thermal image providing step includes providing a measurement's thermal image, which is an infrared thermal video for measuring. The measurement result generating step includes generating a measurement result of at least one physiological parameter of the subject according to a plurality of signals of the forehead block, and the mask block or the nasal cavity block.