A simple and accurate method has been developed to optimize the performance of coaxial couplers for traveling-wave tubes using a 3-D electromagnetic field simulation code. The new technique, which is a combination of numerical and analytical procedures, is presented with a comparison with conventional practice. By using this method, a number of couplers with Sub- Miniature A, Threaded Neill-Concelman, and waveguide output for different tubes were modeled, validated by the experimental cold test data, and optimized. The use of this technique can reduce the optimization time by up to 90% in comparison with the conventional numerical only approach.