With the rapid development of the Fengyun meteorological satellite project, the number of observation channels is increasing, and time and space resolution is enhanced. The original bit rate has been rising from tens of megabits per second to hundreds of megabits and soon will reach over gigabit. The main task of satellites is to obtain remote sensing data. From a certain point of view, satellites could be valued according to the quality and size of remote sensing data. The most crucial part of the Fengyun satellite observation system and satellite-earth-interface is transmitting original data to the ground station through the radio carrier and accurately demodulating the data from those carriers. And this is also the basis of data processing and services. In order to improve the demodulation performance, this article discusses the principle and method of realizing for following important modules: highspeed digital signal processing technologies, the designing of the overall structure of digital demodulation, and the analyses of carrier recovery, cross-polarization cancellation, clock recovery and equalization. Under laboratory conditions, 8PSK digital demodulation systems have been implemented using VHDL. While the data transmission rate reachs 1.2 Gb/s by adopting 7/8 LDPC decoding. And this strongly verifies the effectiveness and superiority of the design in highspeed digital signal processing. It also provides evidence for the development of the Fengyun satellite and the modulation/demodulation of meteorological satellites in the future.