Recently, environmental pollution in hydraulic fracturing operations in the petroleum and gas industry has drawn more and more attention. As a result, research in non-toxic, ultra-low density and high pressure proppants, which do not rely on the environmentally harmful suspending agents used in most fracturing fluids, has become a hot topic. Here, we report the successful preparation of porous proppants with an ultra-low density of 1.25 g/cm(3), a breakage ratio of 6.9%, a short-term fracture conductivity of 102.15 mu m(2) cm and a permeability of 163.57 mu m(2) at 52 MPa synthesized by instant sintering through thermal plasma and closed-external pore sintering using a rotary kiln. The mechanism of forming porous proppants with hard shells and closed pores is described. The concentration of micro-silica, sodium metasilicate, and nano-silica, as well as the sintering temperature in the process of post-sintering, are discussed in terms of their effects on the structure and constituency of the proppant, which determine its mechanical properties. Our study demonstrates that porous proppants without toxic suspending agents are a viable technology for the hydraulic fracturing fluid.