In this paper, a dual-function dynamically tunable metamaterial absorber is proposed. At frequency points of 1.545 ㎔ and 3.21 ㎔, two resonance peaks with absorption amplitude of 93.8% (peak Ⅰ) and 99.4% (peak Ⅱ) can be achieved. By regulating the conductivity of photosensitive silicon with a pump laser, the resonance frequency of peak Ⅰ switches to 1.525 ㎔, and that of peak Ⅱ switches to 2.79 ㎔. By adjusting the incident polarization angle by rotating the device, absorption amplitude tuning is obtained. By introducing two degrees of regulation freedom, the absorption amplitude modulation and resonant frequency switching are simultaneously realized. More importantly, dynamic and continuous adjustment of the absorption amplitude is obtained at a fixed resonant frequency, and the modulation depth reaches 100% for both peaks. In addition, the sensing property of the proposed MMA was studied while it was used as a refractive index sensor. Compared with other results reported, our device not only has a dual-function tunable characteristic and the highest modulation depth, but also simultaneously possesses fine sensing performance.