Pipeline size measuring device

The invention relates to the technical field of pipeline measurement, in particular to a pipeline size measuring device, which comprises a cross rod, clamping frames, a first bidirectional threaded rod, an oil cylinder, a first adjusting box and a rotating motor, wherein an oil cavity and a cavity which are communicated with each other are arranged in the cross rod, a graduated scale is arranged on the cross rod, a first piston is movably arranged in the oil cavity, a first movable rod is arranged in the cavity, the first movable rod is connected with the first piston and is provided with a pointer pointing to the graduated scale, the oil cylinder is arranged in the first adjusting box and is communicated with the oil cavity through an oil pipe, the first bidirectional threaded rod is rotationally mounted in the first adjusting box, the rotating motor is connected with the first bidirectional threaded rod, the number of the clamping frames is two, each clamping frame is connected with a first moving block, th