The invention provides a fully-spherical projection objective which is used for forming an image of an object plane into an image plane. The fully-spherical projection objective, along the direction of an optical axis, comprises a first lens group, a second lens group, a third lens group, a fourth lens group and a fifth lens group; and in a sequence of the incident direction of a light beam, the first lens group G1 has a positive focal power, the second lens group G2 has a negative focal power, the third lens group G3 has the positive focal power, the fourth lens group G4 has the negative focal power, and the fifth lens group G5 has the positive focal power. All lenses in the fully-spherical projection objective are spherical lenses, not aspherical lenses. By adoption of the fully-spherical projection objective, aberration can be better compensated, imaging quality is improved, system resolution is improved, and photoetching efficiency is improved.