The inner superconducting coil of the China Fusion Engineering Test Reactor (CFETR) central solenoid model coil (CSMC) is made of Nb₃Sn conductor of the Cable-in-Conduit Conductor (CICC) structure. After winding the model coil into shape, it is heat-treated by gas protection. The flow resistance of shielding gas in the coil is studied by means of theoretical calculation and experiment. The pressure drop test system mainly relies on the CSMC heat treatment atmosphere protection subsystem as the experimental platform. High purity argon was used as the working medium in the heat treatment experiment, and the pressure drop at the inlet and outlet of the coil was measured at different flow rates and temperatures. The flow resistance of argon in Nb₃Sn coil during heat treatment is estimated by the empirical formula of CICC conductor pressure drop. The experimental results are in good agreement with the theoretical calculation.