The invention provides a coincidence judgment circuit of a positron emission tomography (PET) detection device as well as an adjusting device and method thereof. Each pair of detector module groups with a coincidence line of the PET detection device is connected with the coincidence judgment circuit, by setting or adjusting a level value outputted by a level generation unit in each coincidence judgment circuit branch, the signal delay time of the coincidence judgment circuit branches of each detector module group is identical, so that a coincidence counting rate between each pair of detector module groups is maximized, a total coincidence counting rate obtained by the detection device of a PET system can be maximized, the sensitivity of the system and the image quality of the system can be improved. Through the adjustment, a peak value of the coincidence counting rate generated by the coincidence judgment circuit of each pair of detector module groups with the coincidence line of the PET system can appear in a same narrower time period.