Tianwen-1 is China's first independent interplanetary exploration mission, targeting Mars, and includes orbiting, landing, and rover phases. Similar to previous Mars missions, the Tianwen-1 orbiter was designed for polar orbits during the scientific mission period but has an exceptional eccentricity of approximately 0.59. We provide the first independent eight-degree Martian gravity field model in this paper, which was developed exclusively by a team working in China with our independent software as well, based on about two months of radiometric Doppler and range data from only the Tianwen-1 mission. This model is independent from the models created by the groups at NASA Jet Propulsion Laboratory and Goddard Space Flight Center in the United States, as well as the Centre National d'Etudes Spatiales in France. Furthermore, in order to optimize the engineering and scientific benefits, we proposed a number of potential orbits for the extended Tianwen-1 mission. In order to solve a higher-degree independent Mars gravity field model, the viability of modifying the perigee height was investigated, with the priority considerations of fuel savings and implementation hazards being controlled.