A B+ tree access method, the B+ tree comprising a first layer, a second layer, and a third layer, and data of the first layer being determined as underlying data, characterized in that the B+ tree access method comprises: Before step, determining a minimum read/write granularity of a Data Center Persistent Memory Module, DCPMM, as a node capacity of the B+ tree; when a B+ tree creation instruction is acquired, determining whether there is an idle underlying tree file mapped to a Dynamic Random Access Memory, DRAM; if YES, storing the underlying data of a B+ tree in the underlying tree file; if NO, creating a new target underlying tree file, and mapping the target underlying tree file to the DRAM, so as to store the underlying data of the B+ tree in the target underlying tree file; wherein the underlying data of the B+ tree is stored in the underlying tree file as separate piece of node data according to a node capacity, wherein an offset address of a node of a next layer is stored in a key-value pair of the separate piece of node data; regardless of whether step S102 or 103 is executed, when a number of layers of the B+ tree is greater than or equal to a preset threshold, storing, in a preset storage area, data of a layer numbered to be greater than or equal to the preset threshold in the B+ tree, wherein data of the second layer of the B+ tree is stored in the DCPMM, and data of the third layer of the B+ tree is stored in a preset hard disk; when a data modification instruction is acquired, determining whether there is node data matched with a node identifier contained in the data modification instruction in the DRAM; if YES, modifying the node data according to surrogate data contained in the data modification instruction, and setting a dirty flag for modified node data; if NO, determining whether there is the node data matched with the node identifier contained in the data modification instruction in the DCPMM; when there is the node data matched with the node identifier contained in the data modification instruction in the DCPMM, modifying the node data according to surrogate data contained in the data modification instruction; when there is no node data matched with the node identifier contained in the data modification instruction in the DCPMM, reading the node data matched with the node identifier contained in the data modification instruction from the hard disk to the DRAM; and completing, in the DRAM, modification of the node data according to surrogate data contained in the data modification instruction, and setting the dirty flag for modified node data, wherein after storing underlying data of the B+ tree in the underlying tree file, the method further comprises: migrating data mapped to the DRAM and set with the dirty flag to the DCPMM according to preset periodic time. Before step, determining a minimum read/write granularity of a Data Center Persistent Memory Module, DCPMM, as a node capacity of the B+ tree; when a B+ tree creation instruction is acquired, determining whether there is an idle underlying tree file mapped to a Dynamic Random Access Memory, DRAM; if YES, storing the underlying data of a B+ tree in the underlying tree file; if NO, creating a new target underlying tree file, and mapping the target underlying tree file to the DRAM, so as to store the underlying data of the B+ tree in the target underlying tree file; wherein the underlying data of the B+ tree is stored in the underlying tree file as separate piece of node data according to a node capacity, wherein an offset address of a node of a next layer is stored in a key-value pair of the separate piece of node data; regardless of whether step S102 or 103 is executed, when a number of layers of the B+ tree is greater than or equal to a preset threshold, storing, in a preset storage area, data of a layer numbered to be greater than or equal to the preset threshold in the B+ tree, wherein data of the second layer of the B+ tree is stored in the DCPMM, and data of the third layer of the B+ tree is stored in a preset hard disk; when a data modification instruction is acquired, determining whether there is node data matched with a node identifier contained in the data modification instruction in the DRAM; if YES, modifying the node data according to surrogate data contained in the data modification instruction, and setting a dirty flag for modified node data; if NO, determining whether there is the node data matched with the node identifier contained in the data modification instruction in the DCPMM; when there is the node data matched with the node identifier contained in the data modification instruction in the DCPMM, modifying the node data according to surrogate data contained in the data modification instruction; when there is no node data matched with the node identifier contained in the data modification instruction in the DCPMM, reading the node data matched with the node identifier contained in the data modification instruction from the hard disk to the DRAM; and completing, in the DRAM, modification of the node data according to surrogate data contained in the data modification instruction, and setting the dirty flag for modified node data, wherein after storing underlying data of the B+ tree in the underlying tree file, the method further comprises: migrating data mapped to the DRAM and set with the dirty flag to the DCPMM according to preset periodic time.