The tilt transition process is a key process for tiltrotor to achieve the transition between helicopter mode and fixed wing mode. The difficulty of tilting transition control is high, and designing a reasonable tilt trajectory is an important guarantee for the aircraft to complete safe tilting. The small tilt twin rotor aircraft is the research object. Through the analysis of the aerodynamic characteristics of the aircraft, a trimmed model-based optimization method for tiltrotor transition trajectory is proposed. Based on constraints and performance requirements analysis during the tilt process, combined with energy consumption and safety indicators, an evaluation function is defined. The complexity of optimization problems is reduced with the model trimming. The tilt trajectory is optimized using the direct point matching method, and the rationality of the tiltrotor trajectory design is verified through simulation. The optimization method has strong real-time performance and can be used for online tilt trajectory planning.