This invention provides a guide for operation, comprising: a long column body, being in a hollow shape, an upper side thereof having a semi-cylinder, a bottom side thereof having a cuboid, and an inside thereof being provided with an elongated slot, in which an interior of the semi-cylinder is in communication with an interior of the cuboid； a wing-shaped part, being in a wing shape, and disposed at one end of the long column body and engaged with one side of the cuboid and extending from both ends of the one side of the cuboid, for grasping during surgery； a limiting piece, being in a ring shape and socketing the other end of the long column body and engaging with the other side of the cuboid, for withstanding the tissues during surgery； and a replaceable expander, being disposed in the elongated slot, for expanding and opening a surgical incision of tissues, wherein the replaceable expander is replaceable with another expander of different dimension in a stepwise manner via the one side of the cuboid proximate to the wing-shaped part and inside the elongated slot, thereby for expanding.
