This study proposes a novel rotor position estimation method for wound-rotor synchronous starter/generator (WSSG). At the starting stage, WSSG needs a resolver to obtain the main machine's (MM's) rotor position. However, the use of resolver increases starting system's complexity, volume, weight and cost. In order to solve this problem, a novel kind of MM's rotor position estimation method is proposed, which considers the structure of WSSG as a resolver. The novel method injects a rotating voltage into MM's stator, detects main exciter's stator current and subsequently processes the current signals to estimate MM's rotor position. Experimental results show that the novel method can estimate rotor position accurately, which are in good agreement with the theoretical analyses and simulation results. Compared to the saliency tracking rotor position estimation method, the novel method does not rely on WSSG's parameters (including MM's saliency), and the signal processing procedures are more simple.