Aiming at the problems that the ballast resistance in the jointless track circuit is easily affected by the working environment and the implementation of field measurement is difficult, the ballast resistance estimation method is proposed. Firstly, according to the two-port network theory, the transmission model of the jointless track circuit under the adjustment state is constructed, and the influence law of ballast resistance and compensation capacitance on the voltage and current value at each end of the track circuit equipment is analyzed by simulation. Secondly, based on field microcomputer monitoring data, the error between the simulated value and the measured value of the voltage and current at each end of the track circuit equipment is calculated. Finally, the particle swarm optimization algorithm is used to estimate ballast resistance value by regarding the track circuit transmission model and the error value as the adaptation function and the algorithm adaptation value respectively. And the results are used for performance verification. The experimental results show that the estimated result of this method is verified and the mean absolute percentage error(MAPE) reaches 14. 31%. Thus, the calculation accuracy of this method is better than that of the rail entry voltage method, which verifies the validity and feasibility of this method.