To form the theory and method of hybrid refractive-diffractive (HRD) optical design that can join to the Chinese conventional optical design system, the primary aberration theory expressed by PWC about HRD systems has been investigated, and the function relation between Seidel sums and P, W, C, between ∞, ∞, ∞ and the diffractive lens structure have been established. Using the PWC primary aberration theory and the ultra-high index design method, the original structure of the achromatic HRD medium-power Lister-type microscope objectives has been obtained. The result shows that its design of Seidel sums tallies with the theoretic value, so the PWC primary aberration theory and the ultra-high index design method about HRD systems proved to be effective. Comparing with the conventional two doublet design, it is shown our hybrid objective has a larger work distance and a higher imaging quality, and is suitable for mass production because the front is a singlet plastic lens.