The invention provides a compound-pendulum up-conversion wave energy harvesting apparatus, comprising a shell floating on the water surface and swinging with fluctuation of waves, a compound-pendulum mechanism rotatably arranged in the shell and rotating with its swinging, a driving gear rotatably arranged in the shell and rotating synchronously with the compound-pendulum mechanism, an electromagnetic power generation mechanism arranged in the shell and configured to be meshed with the driving gear for transmission to generate electricity through electromagnetic induction, and a piezoelectric power generation mechanism arranged in the shell and configured to be deformed during its rotation to generate electricity through piezoelectric effect. When the shell swings un-directionally with fluctuation of the waves, the compound-pendulum mechanism makes un-directional rotation that adapts to the dynamic changes of water surface wave energy. The electromagnetic power generation mechanism and the piezoelectric power generation mechanism convert energy through two different electromechanical coupling transduction mechanisms.