Abstract: An X band space-borne spot beam data transmission horn antenna is introduced in this paper. This novel corrugated horn antenna profile is composed of several axial corrugates and vertical corrugates. The axial corrugates feed the vertical corrugates with appropriate proportion of high-order modes to achieve excellent radiation and matching performance. The CHAMP based on mode match technique(MMT) and ‘minimax optimiser’ have been applied on the antenna to obtain best performance. The measured results show that the antenna obtain good performance of gain,return loss and circular polarization over the whole bandwidth between 8. 0 GHz -8. 5 GHz, the edge of coverage (EoC) gain is more than 21. 81 dBi, return loss is less than -27. 8 dB, lower EoC cross-polar discrimination (XPD) is less than -34. 04 dB,the sidelobe is less than -27. 19 dB, the antenna has broad application prospects in LEO satellite.