This textbook contains the contents coming from hydraulics, hydrodynamics, chemical principles, chemical reaction engineering and bioengineering, which relates closely with fundamental principles in environmental engineering. It mainly covers principles including basic concepts, theories, methods and related equipment in fluid flow and transportation, heat transfer, absorption, chemical and biological reaction kinetics and reactors, as well as their applications in environmental engineering. At same time, the readers learns the basic viewpoints and methods commonly used in engineering technology, such as balance method, reasonable simplification, dimensional analysis method, boundary layer theory, optimization and mathematical model method. It broadens the student's understanding in solving those problems in environmental engineering, and enhances their awareness of industrialization. This book is the specialized foundation and principles for learning the professional courses of environmental engineering, such as "water pollution control, " "air pollution control, " "solid waste treatment and disposal" and "ecological restoration engineering", while avoiding the repetition of the contents of those professional books.