Abstract: The steam generator exists the serious false water level phenomenon in a transient disturbance. The difficulty of controlling water level in the low power increases. In order to study the low power water level control problem of steam generator, a time-varying linear parameter change model was established by using linear parameter change theory. A fractional order controller for the steam generator model was proposed based on this model. According to fractional calculus theory, fractional order PI^λD^μ was adopted. Oustaloup indirect discretization method was used to realize the fractional order PI^λD^μ control and the Oustaloup method was improved. The influence of four order parameters of inner-loop and outer-loop and two parameters of the improved method varying on system control performance was studied when the load changed. In different power intervals, the simulation experiments of the improved cascade fractional PI^λD^μ controller were carried out in the case of the same load change. The analysis result shows that the designed improved cascade fractional PI^λD^μ controller can resist interference effectively. The four order parameters of inner-loop and outer-loop and two parameters of the improved method varying influence control effect to a certain degree. Adjusting the parameters reasonable can improve the transient characteristics of the system obviously.