Abstract: The multi-branch horizontal wells can improve the reservoir dynamic flow profile, restrain water coning, enhance production and recovery efficiency due to large drainage area and low cost, and it is significant importance for academic research and industrial applications. However, the effects of branches interference and wellbore variable mass flow on transient dynamics of water breakthrough, production characteristics and recovery efficiency have long been ignored. To dynamically simulate and evaluate the fluid flow behavior of multilateral horizontal wells, first, the branches interference and coupled relationship between reservoir fluid seepage and wellbore variable mass flow has been investigated in this paper, a coupled model for predicting multilateral horizontal wells dynamic production and water breakthrough time is proposed with arbitrary three-dimensional spatial distribution. Subsequently, the model is validated by comparing the production and breakthrough time between actual production data and simulated software. Last, the performance characteristics including inflow dynamics, production, wellbore pressure drop and water breakthrough dynamic distribution are analyzed. The results indicate that the unstable flow time is shorten and it is about 0.6 h, and the wellbore inflow profile represents a characteristic of “low in the middle and high at both ends” on account of branches interference. The pressure drop of wellbore is mainly affected by friction, and other pressure drop types are acceleration pressure drop, convergence pressure drop and mixed pressure drop in order of influence, respectively. The breakthrough time is prior at junction of main wellbore and branch wellbores, then the bottom water spreads to the middle position of main wellbore and trailing position of each branch wellbore. The branch length has a critical impact on breakthrough time, and the branch numbers also affect it as well as the branch angle. The proposed theoretical model can be used to calculate and predict the production, breakthrough time and recovery efficiency of multilateral horizontal wells, and it supplies strong technical support for further development and enhance oil recovery of bottom water reservoir and actual oil field production.