The invention discloses a data replacement method and system, and the data replacement method and system are applied to an XML database. The data replacement method comprises the following steps: finding a target address of to-be-replaced data; detecting whether old value data same as the to-be-replaced data in the aspect of name exists on the target address; if the old value data exists on the target address, replacing the old value data by the to-be-replaced data; and if the old value data does not exist on the target address, inserting the to-be-replaced data into the target address. According to the data replacement method and system, the querying and updating are inserted and combined into one operation; when the data needs to be replaced, the user only needs to find target address, detect whether the old value data same as the to-be-replaced data in the aspect of name exists on the target address, update the data if the detection result is positive and inserting the data if the detection result is negative, so that one operation of finding the target address is decreased, the processing performance of the system can be enhanced, and the transaction concurrency can be improved to a certain extent.