Large-scale renewable energy transmission from desert, Gobi and wilderness to load centers is critical measure to achieve the goals of "Carbon Peak and Carbon Neutrality". Two large-scale renewable energy ultra-long-distance transmission schemes are introduced, including line commutated converter based high voltage direct current (LCC-HVDC) and voltage source convert based high voltage direct current (VSC-HVDC). The two schemes are compared in terms of their applicable scenarios, overvoltage, voltage and reactive power adjustment capabilities, and economy, to highlight their respective advantages and disadvantages. VSC-HVDC is superior in terms of technology and economy. An integrated design scheme of ±800 kV/10 GW four-terminal VSC-HVDC system for 10 gigawatt renewable energy ultra-long-distance transmission is proposed, which includes the electrical main wiring, main circuit parameters, coordinated control strategy, and the configuration of AC/DC choppers. Key technologies such as bipolar single-valve and high-low valve scheme selection, AC voltage coordinated control of multi-valve at the sending end, and DC voltage balance control of high-low valve are studied, and the configuration scheme and switching strategy of the configuration of AC/DC choppers are proposed. The effectiveness of the HVDC transmission system scheme is verified through electromagnetic transient simulation.