A cantilevered piezoelectric coupled energy harvester with variable cross section is proposed to obtain the electric power from the longitudinal motion of the near‐shore sea wave. In order to describe the practical process of the sea wave energy harvesting, a mathematical model of the harvester is established based on Airy linear wave theory and Bessel equations to calculate the output charge, voltage, current, and power. Compared to traditional cantilever harvesters with uniform cross section, this harvesting device has a larger energy harvesting efficiency for its more uniform and bigger surface strain in the action of the sea wave. The computation results show a root mean square (RMS) of electric power of 132.6 W can be reached up with the cantilever height, the wave height, and the wavelength of 2.5, 2, and 12.5 m, respectively, which is 2.41 times of those of the traditional cantilever harvester with uniform cross section. In addition, the output powers of the harvester in tiding and in array are also discussed. This research provided a new practical and efficient method of harvesting near‐shore sea wave energy to supply the electric power demand of the households near seaside.