A tunable piezoelectric driven resonant mass sensor based on modal localization is proposed to detect the external mass disturbances in this paper. The detection structure of the mass sensor is composed of two cantilever beams with different lengths connected by mechanical coupling beams. Firstly, the theoretical modeling of asymmetric resonant element driven by piezoelectric actuator was carried out by using Hamiltonian principle and solved by Galerkin method. The vibration characteristics of the first two modes were obtained. The natural frequencies obtained by the theoretical solution are basically consistent with the COMSOL simulation analysis and experimental data comparison. Different experimental studies have shown that the detection range of the resonator without tuning mass was 2~10 mg, and the detection range of the resonator with tuning mass was increased to 1~13 mg, and the resolution of quality detection was also optimized. In addition, the nonlinear analysis of the structure of the sensor was carried out, and it was found that the detection sensitivity of the resonator under super harmonic vibration has been improved by 80%, which provided a basis for the design of the nonlinear resonance sensors.