The periodic pigging of oil and gas pipelines for dewatering, cleaning and inspection has become a standard industry procedure. The probe pig is the most typical tool for contact-testing in oil and gas pipelines. The dynamic behavior of the probe as it inspects convex defects has been investigated using a home-built inspection system. The probe dynamics differed in the uphill and downhill sections, and the trajectory of the probe was asymmetrical. A bouncing phenomenon was found in the exit region of the convex defect. The experimental results indicated that both the speed and the spring pre-tightening elastic force are closely related to the inspection precision. This study provides a reference for analyzing probe dynamic behavior and improving its inspection precision.