Abstract: The point kinetics is very important to the safety of the reactor operation. However,these equations are stiff, with very small time step for solution. The diagonally implicit Runge Kutta（DIRK）with exponential transformation is studied for point kinetics. It keeps the advantage of diagonally implicit Runge Kutta method which is suitable for stiff equations and owns the better performance than the diagonally implicit Runge Kutta method when the positive reactivity is inserted. Several cases, such as step, ramp, and sinusoidal reactivity insertion are used to show that this method owns high accuracy.