The invention relates to preparation of metal-base composites, in particular to a method for manufacturing a SiC long fiber reinforced Al-base alloy composite through the accumulation theory. According to the method, the atomic accumulation theory is adopted to establish a calculation equation, the relationship between SiC long fibers and Al particles is optimized, and the filling quantity of theSiC long fibers is adjusted through the change of r/R. The problems of accumulation, defects and the like during reinforcing of the composite through the Al particles and the SiC long fibers are effectively solved, and reaction substances of an interface formed between SiC and Al is effectively controlled not to excessively lower the overall mechanical properties of the composite. The SiC long fiber reinforced Al-base alloy composite is manufactured through a low-pressure pressurizing method, the Al particles and molten Al-base are added to be mutually dissolved in a manufacturing technology,the required pressure intensity is lowered, and the production efficiency is improved.