Abstract: A single objective lens with numerical aperture of 0.85 is designed as the coral component of the super high-density optical disk system,which is done with three tools respectively,i.e.two business optical design softwares Zemax and CodeV and the latest CEDDA(characteristic equations discretely defined aspherics)method.The design adopts the latest form of the single bi-aspherical lens in the world with the consideration of decenter error in the manafacture,field error in the application and a reasonable structure in practical application.So that the objective lens has a RMS wavefront error less than 1/30λ and meets the technical requivement.