The retention coil of liquid fuel thorium-based molten salt experimental reactor is an important nuclear safety equipment in the tail gas treatment system of molten salt reactor, which provides a closed environment for the decay of short-lived nuclides in the tail gas, removes the decay heat at the same time, and reduces the temperature of the iodine adsorption bed and the activated carbon adsorption bed downstream it. This paper introduces the problems existing in the original design scheme of the retention coil of the 2 MWt liquid fuel thorium-based molten salt experimental reactor provided by the owner and the new design scheme after structural optimization. The optimized design scheme of retention coil has the advantages of good heat dissipation, few leakage points (few welds), easy welding, easy inspection, monitoring and maintenance, less materials, etc., and has good reliability and economy.