This study systematically investigates structural optimization strategies for cantilever-type piezoelectric energy harvesters to enhance electromechanical conversion efficiency. By developing a multiphysics-coupled finite element model on the COMSOL platform, we analyze the effects of key parameters including mass block configurations, clamping conditions, and auxetic structural designs on output performance. Comparative experiments reveal that unclamped piezoelectric patches at the fixed end achieve 19.98% higher volumetric output voltage (0.1285 V/mm3) compared to clamped configurations, albeit at the cost of increased stress concentration risks. The symmetrical upper and lower clamping design can reduce the stress gradient while maintaining a stable voltage output. Gradient adjustment of y-axis mass distribution demonstrates non-monotonic coupling effects. The adjustment of the gradient of the z-axis mass distribution does not significantly affect the output curve of the energy trap. Notably, negative Poisson's ratio auxetic structures exhibit no significant performance enhancement over traditional triangular cantilevers. The findings provide critical insights into balancing energy output optimization with mechanical reliability, offering a design framework for self-powered monitoring systems in IoT and industrial applications.