In order to realize the perfect absorption of 3~5 μm mid-infrared wave, a tunable mid-infrared broadband absorber based on W/VO2 periodic nanodisk array is designed in this paper. The effects of structural parameters on the absorption performance are calculated by the Finite-Difference Time-Domain. With the optimal structural parameters, the absorber is polarization-independent and exhibits wide-angle absorption. The absorptivity is over 99% in the range of 3.1~3.6 μm, and the maximum absorptivity is 99.99%. At low temperature, the absorber presents a perfect absorption because the magnetic field is trapped in the center of each cell's VO2 dielectric layer. While at high temperature, the VO2 film is converted to metallic phase in which the absorber displays a strong reflection. The absorption difference between high and low temperature is up to 78.8%. The absorber effectively compensates for the shortcomings of the traditional absorber with a narrow absorption band and inability to regulate the absorptivity. The result of this study is of valuable reference to the application of mid-infrared optoelectronic devices.