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This paper represents the application of finite element analysis for the strain wave gear with modified conjugate tooth surfaces. The unmodified tooth profile is designed at a cross section derived from the fundamental kinematic model of the strain wave gear. The conjugation of the tooth profiles has been verified by the plane stress finite element model. Under nominal load condition, the flexspline has elastic deformation comparing with its unloaded shape. The flexspline tooth surface is longitudinally crowned to have a localized contact pattern. Such longitudinal crowning amounts are determined from the deformation of the flexspline, in order to avoid assembling interference under no load condition. To analyze the contact pattern under nominal load condition, the finite element model of manufactured tooth surfaces with modification is established. The simulation results show that no severe stress edge contact exists for the modified strain wave gear. And the simulation results are compared with experiments of contact pattern for verification.