Provided is a manufacturing method of an SiC composite substrate 10 that comprises a single crystal SiC layer 12 on a polycrystalline SiC substrate 11, wherein, after manufacturing a single crystal SiC layer supporting body 14 by providing the single crystal SiC layer 12 on one surface of a holding substrate 21 comprising Si, a polycrystalline SiC is deposited on the single crystal SiC layer 12 through chemical vapor deposition to manufacture an SiC laminated body 15 laminated with the single crystal SiC layer 12 and the polycrystalline SiC layer 11 having a thickness t on the holding substrate 21', during which time, the single crystal SiC layer supporting body 14 is heated at a temperature less than 1,414 degrees Celsius, and a portion of the thickness t of the polycrystalline SiC is deposited, and subsequently, while raising the temperature to 1,414 degrees Celsius or higher to melt at least a portion of the holding substrate 21, the polycrystalline SiC is further deposited until the thickness t is reached and then cooled, and thereafter, the holding substrate 21' is physically and/or chemically removed. According to the present invention, an SiC composite substrate having a single-crystalline SiC layer with good crystallinity and less warpage can be obtained by a simple manufacturing process.