It analyzes the interactive behaviors between external environment and actors (human or an animal)，and their concrete applications in design practice or case studies. Based on the theory of Affordance，it analyzed the interactive relationship between human and external environment in order to understand design objects， affordance， that is， whether they could really meet users′unconscious needs， and whether their functions could adapt to users′unconscious behaviors or not. Furthermore， the activeness of external environment and affordance is analyzed by means of concrete design case studies about product，interface，and culture. We conclude that the external environment has characteristics of activity， and has induction forces towards human′s unconscious behaviors. These induction forces of environment can be criteria for evaluating whether the design is good or not. Good design can well pick up design objects′affordance under human′s unconscious conditions， and good affordance should not be imposed by the designers. The theory of Affordance is helpful to find users′real and potential needs， and can contribute to get appropriate visual form for design innovation till to realize good design.