Structural radar absorber has important application in stealth field for its ability of effectively absorbing incoming radar wave and bearing load at the same time. Metasurface absorbers can achieve near-perfect absorption of radar wave, and have characteristics of light weight and thin structure, but their bandwidth are usually narrow. To solve this problem, this paper proposes a new method to broaden the bandwidth of metasurface absorber. With hybrid integration of varactor and PIN diode, continuous tunning and discrete switching are combined together to broaden the effective absorption bandwidth of the absorber. Using this method, an ultra-wideband tunable metasurface absorber is designed and the absorbing mechanism is analyzed in depth. By changing the bias voltages of PIN diodes and varactors, the absorbing frequency can be continuously tuned within a wide band from 4.57 GHz to 8.51 GHz. Measured results verify the low RCS characteristics of the absorber and the effectiveness of the design method. The proposed method is simple and feasible, and can be extended to other broadband structure design.