A data synchronization method for synchronizing data between a first system and a second system both installed in a first device and both arranged to be accessed by an application, wherein the first and second systems comprise an open system, an open system being a system with a storage area that can be accessed by other applications irrespective of authentication, and a closed system, a closed system being a system with a storage area that can only be accessed by authenticated applications, and wherein the data stored in the two storage areas together is complete data corresponding to the application, the method being performed by the first device and comprising: retrieving (S101) data corresponding to the application from a storage area corresponding to the first system; sending (SI02) the data to a second device for the second device to process the data; upon receiving processed data returned by the second device: temporarily storing the processed data in another storage area independent from the storage area corresponding to the first system and the storage area corresponding to the second system, and then starting (S103) the second system and causing the first system to hibernate; storing (SI04), through the second system, the processed data into a storage area corresponding to the second system; and repeating the above steps (S101, S102, S103, S104) for the first system, with data corresponding to the application from the storage area corresponding to the second system, so as to synchronize data between the first and second systems such that each of the two storage areas backs up the data stored in the other storage area, so complete data corresponding to the application is stored in both the storage area corresponding to the open system and the storage area corresponding to the closed system. retrieving (S101) data corresponding to the application from a storage area corresponding to the first system; sending (SI02) the data to a second device for the second device to process the data; upon receiving processed data returned by the second device: temporarily storing the processed data in another storage area independent from the storage area corresponding to the first system and the storage area corresponding to the second system, and then starting (S103) the second system and causing the first system to hibernate; storing (SI04), through the second system, the processed data into a storage area corresponding to the second system; and repeating the above steps (S101, S102, S103, S104) for the first system, with data corresponding to the application from the storage area corresponding to the second system, so as to synchronize data between the first and second systems such that each of the two storage areas backs up the data stored in the other storage area, so complete data corresponding to the application is stored in both the storage area corresponding to the open system and the storage area corresponding to the closed system. temporarily storing the processed data in another storage area independent from the storage area corresponding to the first system and the storage area corresponding to the second system, and then starting (S103) the second system and causing the first system to hibernate; storing (SI04), through the second system, the processed data into a storage area corresponding to the second system; and repeating the above steps (S101, S102, S103, S104) for the first system, with data corresponding to the application from the storage area corresponding to the second system, so as to synchronize data between the first and second systems such that each of the two storage areas backs up the data stored in the other storage area, so complete data corresponding to the application is stored in both the storage area corresponding to the open system and the storage area corresponding to the closed system. <EOS>