A method for automatic snapshot includes obtaining the amount of data written into a source Logical Unit Number (LUN) and performing increment accumulation; and taking a snapshot when a value of the increment accumulation exceeds the upper limit value. An apparatus for automatic snapshot is disclosed. In one embodiment of the invention, snapshots are taken according to the size of a data variable, only two characterizing parameters, an upper limit value and an increment value need to be added, and the determination logic is clear and concise. Thus, system efficiency or resource overload is not affected, the pertinence is strengthened, the resource usage is increased, and the adaptability is strengthened. Furthermore, stored data may be automatically protected with snapshot, and data safety and reliability are greatly improved.