Abstract: In this paper, one novel thermosetting liquid precursor for SiC was prepared (hyperbranched polycarbosilane, Tri-ImPCS, with viscosity about 3 000 mP·as at 25℃), and fast net shaping of carbon fiber/SiC composites (CF/SiC) by high pressure injection was primarily investigated. Liquid epoxy RE1820 (viscosity about 500 mP·as at 25℃) acts as effective curing agent of Tri-ImPCS, and thermal cure could proceed at room temperature or comparably low heated conditions (<100℃); thermal pyrolysis of thermally cured precursor under atmospheric pressure results into a non-foamed and shape-changeless ceramic monolith. The ceramic yield of Tri-ImPCS under N₂ atmosphere is as high as 74.8% at 900℃ (based on the cured precursor). C and Si elements are uniformly distributed at micro-scale with the atomic ratio of 1.26. Using a joint-process of prepreg molding and high-pressure injection, the fast manufacturing and rapid densification was successfully realized in CF/SiC's processing. The liquid precursor of Tri-ImPCS is an ideal candidate of SiC precursor of SiC matrixed composites.