A new mathematical model was developed to predict the residence time distribution (RTD) of tubular loop reactors. A set of partial differential equations was proposed by applying the axial dispersion model to each section including two tubular sections and a recycle pump. The recycle pump was characterized by the equivalent length and Peclet number. The model parameters were determined through tracer experiments of each section. The fitting formulas of the Peclet number against Reynolds number, pipe length, and mean velocity were obtained. A numerical solution with second-order accuracy was acquired by finite difference method in the time domain. The new model was verified by tracer pulse experiments of the loop reactor. As expected, the model predictions agree very well with the experimental data at different recycle pumps and recycle ratios. The new model predicts the RTD of tubular loop reactors precisely and can be applied to various recycle pumps. With higher predictability and generality, the new model outperforms other existing models.