The invention provides a variable-length connection rod for a small-power engine. The end, facing a second connection rod part, of a first connection rod part and the end, facing the first connection rod part, of the second connection rod part are both of L-shaped structures, one end of the first connection rod part and one end of the second connection rod part are oppositely inserted to each other, the opposite sides of the two ends are provided with racks correspondingly, and a gear is arranged between the two racks; and the end of the first connection rod part and the end of the second connection rod part are both provided with positioning pins, the gear is provided with a rotating shaft, the first connection rod part and the second connection rod part are provided with spring seat correspondingly, and the spring seats are provided with stretchable elastic force mechanisms. Compared with the prior art, when the engine generates knocking of different degrees, a piston changes the stretchable length of the connection rod to different extents, the piston is pushed back and forth continuously, the piston is pushed out at the moment of knocking and then is pushed back, the instantaneous interaction force between a piston head and the connection rod is great, damage is caused in the long run, and through the separated connection rod structure, the action force between the piston head and the connection rod can generate a hydraulic buffering effect.