Abstract: The nuclear power plant pressurizer pressure control system has the characteristics of complex nonlinear and time-varying.On the basis of the theory of fractional order,fractional order PI^λD^μ controller is introduced on this kind of system,to realize the PID control from the point to the surface.Meanwhile,we introduced short feedback algorithm to achieve more precise control.A fractional order PI^λD^μ controller has 2 more degrees of freedom than the classical PID controller and a indirect algorithm（Oustaloup algorithm） was used to implement the fractional order controller.For the fractional-order PI^λD^μ controller parameter tuning,we introduced a biological heuristic algorithm-chicken swarm optimization algorithm（CSO）.Considering the problem that the original chicken swarm optimization algorithm easily falls into local optimum because of the premature convergence,an improved chicken swarm ptimization（ICSO） is proposed.In the algorithm,we changed the chick position update equation,and chaos initialization and random weighting were introduced to improve the accuracy of the algorithm,and to obtain the global optimal.The simulation results show that the FOPID with CSO algorithm has better performance and anti disturbance ability after optimization.