The invention discloses a changeable parallelogram crawler-type in-pipe mobile operation robot. An existing pipe robot adapts to diameter change and angle change of a pipe only through a buffer mechanism, and the adaptive capacity defect exists. The changeable parallelogram crawler-type in-pipe mobile operation robot comprises a vehicle body module, double-slide-block suspension modules, and three changeable parallelogram crawler modules. The three changeable parallelogram crawler modules tightly press the inner wall of the pipe, each changeable parallelogram crawler module is connected with the vehicle body module through one double-slide-block suspension module, and the changeable parallelogram crawler modules spread or contract relative to the vehicle body module. Each double-slide-block suspension module comprises two double-slide-block mechanisms oppositely arranged, wherein each double-slide-block mechanism comprises a first crank, a first connecting rod, a second crank, a second connecting rod and a slide sleeve. The changeable parallelogram crawler-type in-pipe mobile operation robot can automatically adjust a crawler shape and accordingly and effectively improves the in-pipe unknown-barrier-crossing capacity and passing ability in various bent pipes and reducing pipes.