Because of the advantages in the improvements of system power density and reliability, position sensorless control has been becoming a research hotspot for machine driving. A comparative study for the low-speed position sensorless startup of doubly salient electromagnetic starter-generator (DSESG) is made in this paper. With a review to the startup performance degradation introduced by the application of sensorless control strategy, as well as to ensure the sensorless operating performance of aero DSESG system, two position sensorless startup methods are investigated detailedly in this paper, including “align and go” which is of rotor position open-loop, and a pulses injection based sensorless startup strategy, the sensorless starting performance is comparatively researched in terms of commutation accuracy, low speeds startup torque, robustness and control strategy integration. Then, combined with the requirement of aero starter-generator system, aero operating environment and the load feature of aero engine, the selection rule of sensorless startup method for aero DSESG system is further studied. Finally, some simulations are made to verify the correctness and the flexibility of this comparative research and the selection method.