A first level buffer chip gates a target second level buffer chip according to a preset mapping relationship, a first chip select signal, and a first higher-order address signal, and forwards a memory access instruction and a lower-order address signal received from a memory controller to the target second level buffer chip. The target second level buffer chip determines a target memory module according to a second chip select signal and a delayed address signal obtained by delays a second higher-order address signal, determines a target memory chip according to the lower-order address signal, acquires target data from the target memory chip according to the memory access instruction, and returns the target data to the memory controller. A cascading manner of a system memory is changed to a tree-like topological form, which avoids a protocol conversion problem, reduces the memory access time.