Based on nonlinear wave mixing,we experimentally propose a scheme for directly generating optical orbital angular momentum[OAM]by a spirally structured fundamental wave interacting with a nonlinear medium,in which the nonlinear susceptibilities are homogenous.In the experiment,the second-harmonic generation of a fundamental wave carrying positive[negative]integers and fractional OAM states was investigated.This study presents a convenient approach for dynamic control of OAM of vortex beams,which may feature their applications in optical manipulation and optical communication.