The invention provides a data compression method in a key-value database. Access method and system, The data compression method comprises the following steps: compressing data; Data compression operation, intercepting a part of bytes of the complete key domain data in the initial key-value data to generate simplified key domain data; generating simplified key-value data based on the simplified keydomain data and the initial value domain data, the complete key domain data having a complete key value, and the simplified key domain data having a simplified key value; Storage operation, storing the simplified key-value data in a key-value database, and storing the key-value data in the key-value database; and storing the key-value data with the Hash mapping address conflict and the simplifiedkey value conflict by using a linear data table, wherein the stored key-value data comprises complete key domain data and corresponding value domain data. According to the method and the system provided by the embodiment of the invention, the memory access performance in the block chain database can be improved.