Abstract: Pipeline reducer is an important cause of failure, which brings huge hidden danger to the oil, gas and other energy substances transport safety. If calipers and intelligent pipeline inspection gauges have insufficient capacity to pass through the reducer, there is a huge risk of jamming when internal inspection of in-service pipelines with complex working conditions is carried out. Tradition mechanical, polyurethane foam pipe cleaners do not have the ability to locate and detect pipeline reducers. In view of the actual needs of high throughput diameter detection of oil and gas pipelines in complex working conditions, the traditional polyurethane foam pipe cleaner was used as a carrier, and the mechanical structure, array sensing, data transfer, data acquisition, storage and export electronic system of the foam diameter detector was designed and developed, and a three-axis sliding experimental platform was constructed, and a non-contact dynamic sweep was carried out for the specimen simulating pipeline diameter change. The results showed that the developed foam reducer pipe cleaner had a 40% diameter of pipe reducer passing capability, and at the same time could detect pipe reducer defects of at least 1.8% diameter of pipe.