The invention discloses a satellite-borne X-band high-speed data transmission system, which comprises a data format processor module, a high-speed modulation transmitter module, a solid-state power amplifier module, a duplexer module, a microwave switch matrix module and a two-dimensional rotationally polarized multiplexing antenna module. The satellite-borne X-band high-speed data transmission system adopts the design of frequency division multiplexing and antenna polarization multiplexing, and the amount of data transmitted in the unit time is doubled or quadrupled. The satellite-borne X-band high-speed data transmission system solves a problem that a satellite data transmission system is low in real-time data transmission rate when transmitting data to a ground station and cannot quickly transmit load data to the ground. The data transmission system implemented by adopting the design scheme can reduce the data transmission time between satellites and the ground, and completes the task of timely transmitting the satellite load data to the ground within the limited time in which a satellite-ground link is visible.