In order to design a tunable linear-to-circular polarization converter in microwave band, an ultra-broadband linear-to-circular polarization converter (LCPC) based on multiphysics regulation is proposed and studied by combining solid state plasma and vanadium dioxide (VO₂) in this article. By using the electric control way to control the states of the solid plasma resonator, the solid state plasma can generate excitation and non-excitation state. By using the temperature (T) control way to regulate the phase transition state of the VO₂ resonator, the VO₂ can generate insulating and metallic state. The purpose of dynamic shift of the proposed LCPC′s operating band can be realized. The polarization conversion rate curve, reflection phase curve, the axial ratio curve and the surface current diagram of the proposed LCPC are analyzed and simulated by the full-wave simulation software HFSS and the effects of parameters r₁ and r₃ on the axial ratio are also discussed. When none of all the solid plasma regions are excited and T < 68 ℃ , the presented LCPC is in No. 1 state. On the basis of No. 1 state, if all the solid state plasma are excited, the presented LCPC is in No. 2 state. Similarly, on the basis of No. 1 state, the presented LCPC will be transformed to No. 3 state when T ≥ 68 ℃. The axial ratio band which is less than 3 dB (3 dB AR band) is 14.3−29.7 GHz (the relative bandwidth is 70%) in No. 2 state. The 3 dB AR bands which are 14.4−23.4 GHz and 28.6−35.9 GHz (the relative bandwidths are 47.61% and 22.64%) show that the proposed LCPC has the ability to shift the working band to high frequency range. When switching the LCPC to No. 3 state, the 3 dB AR bands which are 8.4−11.2 GHz and 18.7−29.5 GHz (the relative bandwidths are 28.57% and 44.81%) are shifted to low frequency region. Compared with traditional LCPC, our design has the advantages of diverse control means, wide bandwidth, flexible design and strong functionality. At the same time, this LCPC presents a new design method and idea for multiphysical field regulated devices.