At present, when using the fractional order variation method and the fractional order non-variational method to solve the quadratic optimal control problem of the fractional order system, the convergence effect of the numerical algorithm is not good enough, the approximation step is too cumbersome, and the calculation takes a long time. And when using the traditional gradient iterative optimization algorithm to solve the quadratic optimal control problem of the fractional order system, the optimization function requires higher problems. In this paper, for a class of deterministic linear fractional systems under the definition of Caputo, firstly, a state feedback controller is designed to solve the quadratic optimal control problem of fractional order systems from the optimization point of view, and then use PSO to find the second time. The optimal value of the type performance index, that is, the optimal control gain of the system, finally, the optimal control law of the system is obtained. The simulation results show that PSO has better convergence effect and better generality than traditional gradient iterative optimization algorithm, and the performance index is smaller. The algorithm is valid and feasible.