The SARS virus origin which obviously differs from the theory of out-space origin and the theory of wildlife origin was theoretically discussed based on principles of pollution-evolution ecology, pathogenesis and infectant characteristics of SARS, and some relevant experimental evidence. It emphasizes on the fact that increasingly combined pollution in China provides a substantial basis for virus evolution. Gene recombination and fusion of more than one virus in ecosystems should take charge with the origin of a SARS virus. In particular, a common cold or influenza virus can acceleratedly changed into a superpower common cold or influenza virus through genetic mutation and gene recombination by increasingly combined pollution. This work can be useful for human beings to overcome SARS in theory.