Due to the time-varying nonlinear characteristic of switched reluctance motor (SRM), it is difficult to establish an accurate mathematical model. When the internal and external disturbances are large, the traditional PID controller cannot meet the requirement of high control performance. To solve these problems, a linear active disturbance rejection control (LADRC) method is used to design the speed controller of SRM. The uncertainty of the nonlinear model and the sudden change of load are synthesized as a total disturbance, and a linear extended state observer is designed to estimate and compensate the disturbance. A second-order Lagrange polynomial interpolation is used to approximate the position trajectory of SRM, thus the instantaneous speed can be calculated. The rotor position is estimated according to the instantaneous speed while SRM is operated under the conduction angular control mode. The simulation result shows that the LADRC controller is superior to the traditional PID controller. Finally, real-time control experiment of a 6/4 SRM is carried out using a DSP28335 board. The results show that the LADRC combined with the second-order Lagrange interpolation speedometer can realize the conduction angular control of SRM with early on/off operation.