The present invention relates to a surgical instrument for an orthopedics medical surgery, and in particular, provides a technical solution of a cutting head of an expansion orthosis. In the present solution, there is an outer bushing a push-pull rod is provided in an inner cavity of the outer bushing two corresponding metal sheet cutting knives are fixed on a top end of the push-pull rod a seal head of the outer bushing is provided on a top end of the outer bushing two strip-shaped cutting knife bulging ports corresponding to the two metal sheet cutting knives are provided on side walls of the outer bushing the two metal sheet cutting knives can bulge out at the corresponding two cutting knife bulging ports a central baffle between the two metal sheet cutting knives is further fixed on the seal head of the outer bushing. The present solution is characterized in that distances between top ends of the two cutting knife bulging ports and the seal end of the outer bushing are different. The present solution further has the specific feature that the difference between the distances between the top ends of the two cutting knife bulging ports and the seal end of the outer bushing ranges from 2 mm to 20 mm.
