The ultra-wideband redshift search receiver (RSR) on Large Millimetre Telescope (LMT), which covers 73 - 110.5 GHz simultaneously, has been built about 10 years ago. Due to the limits in the speed, performance and cost of the high speed sampler when the receiver was designed, the receiver was implemented using analog autocorrelator. As the price-performance rate in digital technologies is constantly improving, replacing the analog RSR receiver by a digital one becomes feasible. The digital system could offer higher frequency resolution and more system flexibility for more advanced science cases. This project was aimed to design and implement digital backend system for RSR. The RFSoC from Xilinx caught the attention of radio astronomy community when first released. RFSoC device has been selected as a core platform for the RSR receiver, as it offer 8x4G ADCs, large amount of programmable logic resources and powerful processor with multiple cores. Therefore, the RFSoC can integrate signal sampling, data processing and transmission and control functions in a single IC, which will be beneficial in both system design and costing perspectives. The talk will be focused on the digital backend system built for RSR and general radio astronomy receivers based on the RFSoC. The system at the present stage is fully functional as a spectrometer and can be extended in any shape base on system requirement of different telescopes and science cases. The experimental ADC characterization demonstrates around 80 dB Spurious Free Dynamic Range (SFDR) over the spectrum from DC to 2.048 GHz. The evaluation results of the RFSoC based spectrometer performs with high level of stability and dynamic range with hundreds of seconds’ real-time integration time. The results give us solid confidence in using RFSoC for radio astronomy receivers. It is a critical milestone of the RSR receiver project and we can carry on by just scaling the system up. The RFSoC based receiver modules will be extend to CBASS, Goonhilly GHY3 and other receiver platforms under development in Oxford. The system is not only suitable for high bandwidth signal but also hugely beneficial for systems with high channel counts, such as SKA, ATA and other interferometry radio astronomy telescopes. The RFSoC data converters can digitize as many as 16 channels simultaneously, the programmable logic can handle the channelization and beamforming and the control and communication can be managed by the applications on ARM processors. It can largely save the system cost and development effort in both hardware and software perspectives.