For the observability of inertial sensor misalignments in inertial platform self-calibration problem, the effects of the system model and platform coordinate frame on observability were analyzed. Based on different system dynamic models and measurement vectors, four system models were built. The observability of inertial sensors misalignments in different models with different definitions of platform coordinate frame was investigated. The theory conclusions and simulation results show that the system is observable only in two conditions: the system measurement models are built up with platform angles and accelerometer triad outputs, the system dynamic model is built up with platform angles and the platform coordinate frame should be defined with the benchmark hexahedron of platform; the system measurement models are built up only with accelerometers triad outputs, the system dynamic models are built up with platform attitude or misalignment models and the platform coordinate frame should be defined with the accelerometer sensor axes. 