Data storage method and device

The invention discloses a data storage method. The data storage method comprises the following steps: when a mobile storage device detects a modification instruction of a data file, determining the data file corresponding to the modification instruction; determining a preset cluster number of the data file in a file directory list; and if the cluster number of the data file in the file directory list is in front of the current marked cluster number, forbidding the modification operation corresponding to the modification instruction, wherein the current marked cluster number is determined according to a maximum critical point of a maximum effective cluster number before the mobile storage device is powered on. The invention also discloses a data storage device. By adopting the data storage method and the data storage device, the data storage security is improved.