Cancer therapy is facing challenges. Since current theory could not have a breakthrough, we ought to find a new way to conquer cancer by exploring the emerging theory in cancer therapy. The complexity science, emerging in the 1980s, is the new stage of the system science development. It raises a series of transformation from humanities to natural science. Dissipative structure theory as a major science of complexity science, when applied to medical field, probable provide opportunity and inspiration referring to treatment. Dissipative structure theory, in brief, claims that a dissipative structure transform chaos to relatively stable non-equilibrium state through non-equilibrium phase transition. From the microscopic order, cancer composed by tumor cells is a dissipative structure, whose external environment is the human body. From the macroscopic order, the human body is a dissipative structure, whose external environment is the natural and social environment. The reason for tumor occurrence and progression is relatively non-equilibrium disrupted and negative entropy is not enough to correct high positive entropy. Survival with the tumor is to enhance negative entropy to resist highly positive entropy and then build a new relative non-equilibrium state. Innovative angle from the theory may enlighten us make the better use of dissipative structure theory in clinical cancer therapy.