The design parameter and formulation for calculating dimension in internal gear pump with straight line conjugated curve profile are discussed at first.Then a mathematic model for optimization of the design parameter of this pump

which takes the minimum fluctuation of flow and maximum flow per cubage of the pump as objective function

and contact ratio

pressure angle

profile overlapping and etc as constraint condition.By comparison the optimized design parameter of the two examples with others of this type of pump

the result is satisfactory and the result can be utilized in design same module and same number teeth.it gives a theory foundation for design of the pump.