The hybrid cascaded UHVDC technology is especially suitable for large-capacity, long-distance and overhead line power transmission, and is one of the important technical approaches to solve the problem of large-scale renewable energy transmission over long distances. This paper establishes the small-signal model of the hybrid cascaded UHVDC system and validates the accuracy of the small-signal model by comparing the step responses obtained from the small-signal model with those from the detailed electromagnetic transient model. Based on the developed small-signal model, the impact of two different control modes of the system, the master-slave control mode and all constant DC voltage control mode, on the small-signal stability is investigated.