Summary Pipes with diameter reduction and direction variation are very common in deepwater extraction. While the high-pressure and low-temperature conditions may trigger severe hydrate problems, current studies on hydrate particle migration and deposition are mainly carried out in pipes with a constant diameter, whereas the law of diameter reduction has been less explored; in particular, the effect of diameter reduction + direction variation in pipe has not been reported. In this study, a model of hydrate particle migration and deposition in special pipelines is established based on the computational fluid dynamics (CFD)-discrete element solver (DEM)-application programming interface (API) method, which can be used to carry out real-time visualization calculations of hydrate particles. Simultaneously, this paper reveals the mechanism of hydrate particle migration and deposition at the diameter reduction and direction variation, which provides a new idea for the design of the pipe. Furthermore, for the pipe with diameter reduction + direction variation, the entire process of deposition blockage is simulated, and dangerous locations of pipe clogging are identified. The simulation results found that there is a maximum hydrate deposition particle diameter (MHDPD) for hydrate deposition in the pipe. The results of this work may provide valuable references for accurate prediction of particle deposition in deepwater development.