Prior to formally equipping an inertial navigation system （INS）， its navigation accuracy must be evaluated based on the national military standards. Owing to the continuous accuracy improvements of the rotary modulation INS， the duration of a single-navigation experimental cycle is increasing， thereby causing challenges to test and evaluate the INS system. Thus， to evaluate the navigation accuracy of a long-endurance rotary modulation INS， first， this study introduces an integrated rotary modulation scheme with self-calibration， self-alignment， and navigation functions that unify the self-calibration and self-alignment state of the INS and the rotation path in the navigation process. Subsequently， this study proposes a long-period navigation test method based on repeated samples for long-endurance rotary modulation INS to improve all required navigation testing and evaluation tasks. Finally， the study obtains and uses 30-day long-endurance navigation laboratory-test data to test and verify the maximum position error （0.71， normalized， which is equivalent to the statistical results of independent voyages）. Furthermore， the effectiveness and feasibility of the proposed method are verified using a vehicle dynamics test. The results show that the proposed method can significantly shorten the test cycle. Thus， this study provides an effective approach for developing and evaluating long-endurance rotary modulation INS.