Abstract: Ultra-low frequency oscillations (ULFOs) related to the governor system have occurred in the actual system. The power system with enhanced dead zone (step dead zone) is a piecewise smooth discontinuous system (Filippov system), and its oscillation mechanism and influencing factors are complex. For the single hydropower system with enhanced dead zone, the non-smooth bifurcation theory was used to analyze the system bifurcation characteristics of the border-crossing equilibrium and non-smooth limit cycle of load parameter under typical dead zone size. The results show that the appearance of switching-type ULFO (ST-ULFO) corresponds to two types of non-smooth bifurcation of Filippov system, the first was the Hopf-like bifurcation with the stable node disappearing (becoming a pseudo-equilibrium on the boundary), which corresponds to the occurrence of ST-ULFO without equilibrium. The second was corresponding to the C-bifurcation on the trajectory. In this case, the system changed from no equilibrium (or a pseudo-equilibrium) to a stable focal equilibrium, but the system trajectory converged to a large-scale stable non-smooth limit cycle, which corresponded to the occurrence of ST-ULFO with a stable equilibrium. Furthermore, the effects of different deadband sizes (changes in non-smooth system structure) on the above two types of non-smooth bifurcations were analyzed. The results show that increasing the deadband can improve the system's ability to withstand load disturbance to a certain extent, which may be beneficial to the system stability.