Abstract: For the requirements of fast reactor controller with faster response speed and higher control accuracy, Linear Active Disturbance Rejection Controllers (LADRC) are designed for the reactor power and the core coolant outlet temperature, respectively. Based on the fast reactor neutron dynamics kinetics and the core heat transfer equations, the second order nonlinear models of the relative power and coolant outlet temperature for the controller design are derived, and the corresponding Linear Extended State Observers (LESO) with model information are designed. The range of LESO bandwidth is chosen via the time scale parameters of the derived second order model. The range of PD bandwidth is estimated by the allowable range of deviation and actuator operating speed, and the LADRC parameter tuning is carried out accordingly. The simulation results show that the LESO with model information has better total disturbance estimation capacity. The designed LADRC all are with faster control speed and higher precision, and the control performances of LADRC using LESO with model information are better.