Using the Moon as an Earth observation platform for remote sensing offers the benefits of a high orbital altitude and vast surface area, which could provide continuous Earth observation capabilities over great temporal and spatial scales. Over the course of China’s follow-up lunar missions in the next three Five-year plans, the Earth observation instruments will be put on the Moon. However, the understanding of the characteristics of Moon-based Earth observations remains limited. Here, the observational characteristics for a moon-based platform related to the Earth ellipsoid model is studied, which advances previous studies with a spherical Earth assumption. We perform three analyses. First, an integrated coordination transformation equation, which denotes the geometric relationship between a Moon-based platform and the target on Earth is established based on numerical ephemerides and Earth orientation parameters. Second, the explicit expression for the intersection between the line of sight of the sensor and the Earth oblate spheroid is formulated, and the formulae of uncertainties are given. Lastly, a theoretical visible area on the Earth ellipsoid observed from the sensor is derived based on the geometrical relationship between the observation position and the Earth ellipsoid; two special situations are obtained via explicit expressions and series expansion. Based on this, the optimum radius for the spherical assumption of the Earth is obtained. The simulation and analyses reveal that the proposed mathematical derivation aimed at the Earth spheroid can be used to improve the accuracy of studies focused on the geometrical characteristics of Moon-based Earth observations.