A storage server system includes a cage, a midplane, a power supply module, a motherboard module, an HDD backplane, and a data HDD. The cage has a first end and a second end. The midplane is fixed inside the cage. The power supply module is disposed inside the cage. The motherboard module is disposed inside the cage and closer to the first end than the midplane. The HDD backplane is detachably disposed inside the cage. The HDD backplane is closer to the second end than the midplane. The data HDD is detachably disposed inside the cage. After the data HDD and the HDD backplane are detached from each other, the HDD backplane is detached from the cage along a detaching direction towards the second end and away from the first end.