A four-fiber collimator based on four-fiber header and a variable-curvature lens has been developed for a novel Reconfigurable Optical Add-Drop Multiplexer (ROADM). The variable-curvature surface consists of two spheres. The four fibers are arranged equidistantly and parallelly in one plane, then four light rays from the fibers pass through different part of the lens so that the angle of output light from the collimator can satisfy the application requirement. When the output facets of fibers are at the object focus of the variable-curvature lens, the light emitted from the fiber could be collimated. By using matrix optics method, the structure parameters of the four-fiber collimator, such as spheric radius and lens length, were obtained. The propagation of light field in the device was stimulated by RSOFT, from which energy concentration over 90% come under observation.