Aircraft braking system is a important subsystem for aircraft safety. Hardware-in-the-Loop (HiL) system is an important process for aircraft braking system study. It can be utilized to study control algorithm and validate the performance of braking before physical experiment which has advantages of low cost and rapid evaluation. In this study, a HiL system of aircraft braking system is established on the realtime operating system of RTX. By analyzing the stress situation of aircraft, the dynamic equations of aircraft, wheel, braking actuator, et. al. are presented. The temperature of braking disc is very important for the braking system, therefore, the thermodynamic equation of braking disc is also considered in the model. The nonlinear characteristics of friction force with slip-ratio and temperature is also modeled to increase the accuracy of the model. The models are a set of nonlinear differential equations which are calculated by the Runge-Kutta method. A subdividing integration step method is introduced to improve the simulation accuracy. The proposed model is validated by an aircraft braking system demonstration. The results indicate that the proposed HiL system has high accuracy and high flexibility which lay a foundation for studying of aircraft braking.