The disclosure is related to a clamp-type measuring device includes a clamp and an interval measuring module. The clamp includes a guiding rail and two holding arm. Each of holding arms includes a guide part, a connecting part, and a clamping part. The guide part is movably furnished on the guiding rail. Both ends of the connecting part are respectively connected to the guide part and the clamping part. The interval measuring module includes a first measuring element and a second measuring element. The first measuring element and the second measuring element are furnished on the two connecting parts respectively. The first measuring element and the second measuring element are slidable through the two guide parts respectively in order to measure an interval between the two clamping parts. In addition, the disclosure is also related to a measuring method of the clamp-type measuring device.