The text analyses some key problems of accurately machining of O circle mould cavity, including its technology, measurement, and machining error, and then puts forward a CAD example for it.

This paper discusses various factors which affect the dimensional torlerence of products of precise mould and offers a multi-object optimal method for designing cavity dimensions of precise mould.

Gas hole and inclusion can be reduced by properly increasing thickness, and quality of the chilling layer, uniformly spraying and cleaning the mould cavity on time.