Two kinds of carbon doped particles, graphene and toner, were used to directionally modify solid propellant. The influence of different doping ratios and working conditions on the divergence angle of the modified propellant was compared and analyzed by high-speed photography technology and a self-built beam divergence angle measurement system, so as to determine the optimal doping ratios and working conditions of the doped particles. It is found that the optimal doping ratio of graphene and toner is 7%, and the beam divergence angle of graphene is smaller, and the response time of generating stable plasma flow is shorter. At the same time, graphene is more suitable for the working conditions under the small laser energy supply, and toner is more suitable for the working conditions under the large laser energy supply.