The invention relates to a double-beam low-frequency rotating mechanical energy collecting device, which is characterized by comprising a first base, a piezoelectric plate, a collection cantilever beam, a first mass block, a second mass block, an excitation cantilever beam and a second base, wherein the first base and the second base are both connected with a rotating mechanism; the left end of the collection cantilever beam is fixed to the first base; the piezoelectric plate is arranged on the upper surface, close to the left side, of the collection cantilever beam; the first mass block is fixedly installed at the right end of the collection cantilever beam; the right end of the excitation cantilever beam is fixed to the second base; the left end of the excitation cantilever beam is connected with the second mass block; and the first mass block is vertically opposite to the second mass block. The device is scientific and reasonable in structural design, the double cantilever beams serve as a basic energy collection structure, the structural setting and the design are simple, and the manufacturing and the maintaining are easy; and the excitation cantilever beam achieves resonance under low-frequency excitation and collides with the collection cantilever beam to excite the collection cantilever beam to deform, and the device can be suitable for low-frequency rotating energy collection.