The application of the System Engineering becomes a new science in the field of Law recently. It is called ”System Theory of Law”. Traditionally, natural science is seperate from Social Science. However, there comes a trend of combining the said two sciences. The subject matter of the present paper is a survey about the trend. This paper includes the followings: (1)The development and contents of the ”System Engineering” theory. (2)The reason why the system Engineering develops so rapidly in mainland China. (3)The philosophical background behind the development of the system Theory of Law in China. It is expected that in Taiwan this paper may hereby call legal scholars' attention to the new theory and reactions may come out consequently.