This paper proposes a new control method for a four-dimensional hyperchaotic system using the terminal sliding mode control. It eliminates the need for the traditional activation function by replacing it with a hyperbolic tangent function. This method effectively deals with the effects of parameter uncertainties and external disturbances in the systems, also eliminates the chattering phenomenon in the synchronous process, enables the response system and the drive system to reach the synchronization state in a fixed time. Finally, numerical simulations with MATLAB software were applied to verify the effectiveness of this fixed time convergence technique.