A shock-absorbing seatpost assembly includes a seatpost, a linkage device, an adjustment device, and a buffering member. The linkage device is connected with an end of the seatpost, and the adjustment device is movably inserted into the seatpost. The adjustment device is provided with a pressure adjusting unit abutted against a pushing member provided at the linkage device. An end of the pressure adjusting unit protrudes outward from the end of the seatpost. The buffering member is disposed inside the seatpost and has an end abutted against the pressure adjusting unit of the adjustment device. Accordingly, the portion of the pressure adjusting unit exposed outside the seatpost provides adjustment of the preload of the buffering member for riders of different body weights.