A method for laser-cutting a carbon fiber substrate such as a preform is configured from fabric material comprising at least carbon fibers, characterized by cutting the carbon fiber substrate at initial conditions which have been set so that the state of the substrate that is being cut with a laser can be suppressed with or prevented from deviating from a target state. By the method, it is possible to effectively solve various problems such as dissipation of heat, positional shifting from the focal length range of the laser, and soot, and the carbon fiber substrate can be stably cut at the target desired state.