To realize the cyclotron resonance at the fundamental harmonic between a 1 THz wave and electrons gyrating in the external magnetic field the magnetic field should be about 38 T. This value is well above what is currently achievable in cryomagnets used in gyrotron experiments (up to 10-15T).The pulsed magnet can generate a high magnetic feld (up to 100T), promoting the development of high-frequency high-power gyrotrons. In this oral presentation, a system of the 40T Flat-top Pulsed Magnet Field for 1THz Gyrotron is introduced.Firstly,a fast cooling and long lifetime 40 T pulsed magnet is developed for a 1 THz gyrotron. Internal cooling channels are introduced to increase the cooling speed without compromising mechanical strength. It is estimated that the lifetime is about 20,000 shots at 40 T. The magnet is capable of realizing a 40 T fat-top pulsed feld (fat-top time 10 ms) with a cool down period of 16 minutes. Secondly,a novel topology, which consists of a sequentially fired pulse forming network (SFPFN) and a coupled inductor active filter, has been developed to generate large current with a high-stability flat-top. Thirdly, a control method based on model predictive algorithm is utilized to compensate the circuit parameters change in a wide range. The thermodynamic models for every circuit state of the topology are built to predict the future value of the state variable. Based on those models, the algorithm of the model predictive control (MPC) is constructed, in which the influence of circuit state transition on the optimal control action is considered. At last, a full-scale system of 10 kV/20 kA is constructed, and the pulsed magnetic field of 40 T/10ms/96 ppm are achieved.This can facilitate the long-pulsed quasi-steady operation of gyrotron operation.