Abstract: The structure and parameters of the cable-in-conduit conductor (CICC) and the operation condition of the Nb₃Sn superconducting magnet used in fusion experimental device in China were introduced. A one-dimensional mathematical model, Gandalf, was used to calculate the pressure drop in CICC under the circulating mode of forced flow cooling which used supercritical helium as coolant, and consequently the relatively reasonable mass flow of liquid helium in theory was obtained.