Abstract In this paper, amplification and saturation properties of one dimensional free electron laser (FEL) operating in Raman regime with helical wiggler and axial magnetic field are studied. In order to investigate and enhance the saturation characteristics of the system, prebunched electron beam is considered which describes the non-uniform initial distribution of the electrons. By using Maxwell’s equations and Lorentz force equation of motion of the beam, a set of self-consistently coupled nonlinear differential equations, describing radiation dynamics and beam trajectories, is derived and is solved numerically by the fourth order Runge–Kutta method. To study the effect of the beam prebunching on the saturation, the linear and non-linear initial distribution of the electrons are considered. Depending on the strength of the axial field, it is found that beam prebunching can reduce the saturation length and enhance the saturation efficiency of the radiation field substantially which can be offered as an effective approach to bring down the cost of the FEL system.