With the development of deep-space exploration, low-density ablators have received increased attention due to their distinguished features such as good ablation performance and low structure weight to fulfill the requirement of lightweight, low ablation rate, low thermal conductivity and long re-entry time of thermal protection for heatshield and backshell of planetary entry probes and re-entry capsules. The historical prospects on development of low-density ablative thermal protection systems and materials were introduced with emphasis on low-density honeycomb reinforced silicon rubber, phenolic and organic silicone resin ablators, as well as the typical representative of light weight ceramic ablators (LCAs) such as silicone impregnated reusable ceramic ablator (SIRCA) and phenolic impregnated carbon ablator (PICA). According to the task requirements of China's new-generation manned spacecraft, including low earth orbit flight mission, as well as manned flights to the Moon, the asteroid and the Mars, the progress of basic and applied research on lightweight thermal protection system for the spacecraft was presented. And then, it analyzes the technology gap between domestic and foreign, and provides several suggestions concerning the prospects of China's low-density ablators.