This paper puts forward the conception of workability reserve, analyzes the relationship among workability reserve, safety coefficient, restrictive condition parameters and reliability , points out the defaults of the traditional method of machine design, which adopts safety coefficient to ensure the security of machinery products,and provides the computation module of workability of mecha.

The paper researches on the relation between the smallest transmutability quantity of work equipments work load attributes or metering equipments work load attributes and the smallest adjustability quantity,and then proposes an essential method to design the control characteristic of the work equipments or the metering equipments.