Functional principle is a special teaching principle based on the physical and mental obstacles of mentally retarded children, the amount of educational restrictions and the basic needs of participating in social life.

Functional principle refers to teaching the most important knowledge and skills necessary to adapt to environmental life to children with mental retardation and helping them to apply them in a specific environment, so as to form functional knowledge and skills needed to participate in social life according to the environment.

The principle of functional teaching requires teachers to pay attention to the application of knowledge and skills in a specific environment, including the application mode and effect, when considering the logic of teaching subject knowledge.

Functional principle is more suitable for children with severe mental retardation, multiple mental retardation or older mental retardation to develop social skills.