This paper presents design of altitude controller for an indoor blimp robot and its realization. Due to hardware restrictions, the altitude control behavior of blimp is modeled as a switched system with time-varying delay. HOSM differentiator is used as an observer for vertical velocity, it is also used in order to estimate the switching signal. Then a predictor-based controller is conceived, its gain is determined by common Lyapunov function method to ensure the global uniform exponential stability of switched system. Control scheme is implemented by Matlab Simulink, finally, the performance of blimp altitude controller is verified in experiments.