Disclosed in the invention is a guaranteed-measurement-precision-based measuring device for engagement depth of circuit breaker contacts. The measuring device comprises six sets of displacement sensors that are installed in counter sinks inside six moving contacts of an A phase, a B phase, and a C phase of a handcart type circuit breaker of a high-voltage switch cabinet. A power line and a signal line are led out from a peripheral gap of a plum-blossom contact and are led out of the high-voltage switch cabinet by the space of the handcart type circuit breaker and then are connected with a data processing device; and the data processing device is connected with a display device. The provided measuring device has advantages of reasonable structure and convenient and accurate measurement.