Addressing the challenge of assessing the accuracy of initial alignment algorithms for rotating inertial navigation systems (RINS), particularly when error magnitudes are small and difficult to evaluate, this study proposes an indirect method for estimating alignment errors. This approach is premised on the error propagation characteristics of strapdown inertial navigation systems (SINS) and utilizes positional errors to appraise initial alignment errors. Grounded in the error distribution algorithm of strapdown inertial navigation, the method analyzes the principal sources of navigational errors during the RINS operation to discern the relationship between navigation positioning errors and initial alignment errors. Subsequently, an indirect measurement technique for initial alignment error is devised to gauge the precision of the RINS initial alignment. Simulations and experimental outcomes indicate that this method can ascertain differences in the accuracy of various alignment schemes without the need for high-precision attitude reference information. The novel accuracy assessment method introduced bears significant implications for the analysis and testing of RINS, particularly in the domain of initial alignment research.