Abstract: The application of small reactors is more flexible than that of large-scale PWRs, which needs to consider the demand of load variation under grid connection and island operation. However, the controlled system of coolant average temperature under rod speed control is non self balancing system, which has strong rigidity, open-loop instability and complex nonlinearity. Improved dynamic matrix controller (DMC) is designed in this paper. The controller widens the scope of the application of the traditional predictive control and overcomes the limitations of the algorithm. By comparing with the program unit control and PI control, it is verified that the steady-state error of the system is smaller, the response speed is faster and the tracking performance is better.