The lateral migration of an elastic capsule under an optical force in a uniform flow was studied by numerical analysis. The capsule was moved through the fluid flow using a laser beam with a Gaussian distribution focused along the direction normal to the flow device surface. Under an externally applied optical force, the initially spherical capsule deformed and migrated laterally. To simulate such a system, a penalty immersed, boundary method was adopted to enable fluid-membrane coupling, and a dynamic ray tracing method was applied to the optical force calculation. The effects of the elastic properties of the capsule membrane (the surface Young s modulus and the bending modulus) on the lateral migration were studied. By increasing the surface Young’s modulus, the capsule deformed less and the migration distance increased; however, buckling occurred in the capsule at a high surface Young’s modulus. Buckling could be suppressed by increasing the bending rigidity. The results show that the migration distance was maximized for a rigid spherical particle under identical conditions.