The invention provides a bimetal composite pipe both-side welding process. The process comprises (1) preparations before welding; (2) matrix bottom seal welding; (3) carbon steel matrix thermal weld bead welding; (4) carbon steel matrix filling and cover welding; (5) anti-corrosion lining slope grinding and cleaning; (6) anti-corrosion lining overlaying. The process has the advantages of being high in welding quality, small in labor intensity, low in construction cost and high in production efficiency and particularly applicable to welding of oceaneering composite vertical pipes, liquefied natural gas low-temperature high-pressure anti-corrosion pipes, oil and gas pipes, heating furnace pipes, chemical pipes and the like and applicable to deepwater composite pipe and pressure containing welding.