费马原理是几何光学的一个基本原理.本文运用费马原理直接推导得到球面界面的发散光线方程，并使用近轴条件得到了相应的虚像物像公式.结果表明发散光线方程与会聚光线方程不同，而物像公式均相同.

Fermat's principle is a basic principle in geometrical optics，which means that the actual trajectory in the space depends on the extremum of the optical path. Based on the Fermat’s principle，a new method has been given to directly obtain the equations for the practical optical path in reflections and refractions at spherical boundary for the virtual image，and then the object-image formula have also been derived in the condition of axial ray and axial object. The present results show the equations for divergent lines are different from those for convergent lines，but their object-image formula are very same.