Abstract: The bulb tubular unit has been used in many small and medium-sized hydro-power stations in our country. This kind of unit has the characteristics of large inertia time constant of water flow, small inertia time constant of unit and double regulation of guide vane and blade. In addition, the guide vane and blade is in a non-co-linked state during load shedding process, so the characteristics are more complex and the control is more difficult. Especially for many small and medium-sized hydro-power units, the load shedding is often caused by lightning strikes in the flood season, which requires faster stable power operation of the unit, and higher requirements for the control of the transition process of load shedding. In this paper, a nonlinear model of the load shedding transition process of bulb tubular turbine is established. The fixed rotor characteristic curve is used to simulate turbine characteristics. The characteristic line method is used to solve the pressure unsteady flow equation, and the governor equation is introduced, a precise simulation of load shedding transfer process is realized. The load rejection transition process of the actual bulb tubular unit is simulated.The maximum speed increase of the unit under the maximum head is greater than the maximum speed increase under the rated head. Maximum pressure at the inlet of guide vane under the maximum water head is greater than the maximum pressure at the inlet of guide vane under the rated water head. The minimum pressure at the inlet of the draft pipe under the rated head is less than the minimum pressure at the inlet of the draft pipe under the maximum head.The overshoot of unit speed control under rated water head is larger; At the initial of load shedding, the negative water hammer characteristic is obvious. The maximum unit speed at 75% rated load shedding is greater than that at 100% rated load shedding. The maximum pressure at the inlet of guide vane at 75% rated load shedding is close to that at 100% rated load shedding. The minimum inlet pressure of the tailpipe under 100% rated load shedding is the minimum. The research results show that for the bulb tubular turbine, due to the small moment of inertia of the unit and the equal opening lines incline to the right, the bulb tubular unit will produce obvious negative water hammer characteristics in the initial load shedding process, resulting in lower pressure in front of the guide vane and higher pressure at the tail pipe inlet. The minimum unit speed is smaller and the overshoot is larger at the rated head condition compared to the maximum head condition under the same control parameters. Because the escape characteristics of turbine are affected by both guide blade and blade opening, the maximum unit speed may occur in the condition of non-rated head shedding partial load condition rather than 100% rated load under the rated head condition. The research results have a guiding significance for the design, operation and maintenance of bulb tubular turbine.