Based on the finding that the inductance of doubly salient electromagnetic motor varies according to its rotor position, a new method to determine the initial rotor position is introduced in this paper. With no extra test pulses needed, this method detects the sector where the rotor is at by comparing the three-phase induced voltages during the excitation field building, significantly cutting down the time required for this procedure. Then, an equation expressing the relationship between rotor position and the three-phase terminal voltages is developed based on geometrical relations of “inductance rectangle” composed of mutual inductances, which gives a more accurate estimation of the initial rotor position. Moreover, in order to avoid the occurrence of rotor jitter or even reverse when the rotor is initially in the boundary of neighboring sectors, the first acceleration pulse for sensorless startup is distinguished from the ordinary ones, and the first acceleration pulse is studied in detail regarding the injection method, pulse width, and a new division of sector boundary. Further experiments confirmed the feasibility of the proposed methods concerning the estimation of initial rotor position and the assurance of anti-reverse rotation startup.