Aiming at the characteristics of VTOL fixed-wing UAV, including high power demand during vertical take off and landing, relatively steady load in fixed wing cruise, and significant power fluctuation under maneuvering conditions, a semi active hydrogen fuel cell lithium battery hybrid power system is established. Based on the system mechanism models, three energy management strategies, namely FSM(finite-state machine), ECMS(equivalent consumption minimization strategy) and ECMS MPC(equivalent consumption minimization strategy model predictive control), are designed and compared under identical simulation conditions. The results show that the maximum mission power demand is 8.83?kW. The ECMS MPC strategy satisfies the full process power requirement with a terminal SOC(state of charge) of 0.3959, which exceeds the lower SOC limit of 0.35. Compared with FSM and ECMS, ECMS MPC yields a cumulative hydrogen consumption of 11.63?g, reduced by 10.73% and 12.11%, respectively; the equivalent hydrogen consumption is 25.95?g, decreased by 1.35% and 2.11%, respectively. The average efficiency of the hybrid system reaches 70.06%, increased by 2.54 and 3.41 percentage points correspondingly. Meanwhile, ECMS MPC raises the operating proportion of the fuel cell within its high efficiency region to 25.29%, representing an increment of 24.79 and 8.32 percentage points over FSM and ECMS. Therefore, the ECMS MPC strategy can optimize the power distribution between the fuel cell and lithium battery while ensuring SOC safety constraints and power tracking capability, reduce mission hydrogen consumption and improve system energy efficiency. It provides a reference for energy management of hydrogen lithium hybrid power systems for composite wing UAVs.