With the rapid development of cloud storage, more and more people prefer to store their owner data in remote cloud storage to avoid troublesome data management in local storage systems. The most famous feature of cloud storage is the concept that storage as a service, users can store their own data into clouds by public APIs. However, because of losing absolute control of data, users storing their own data in cloud storage will suffer a series of security problems, such as data peeping, data tampering, and so on. In order to solute those security problems and improve the quality of secure cloud system based on enhance its security, researchers have investigated lots about cloud security problem in recent years, which established a research branch of the cloud storage- -secure cloud storage system. This paper introduces the security demand of secure cloud storage system; expounds the current status of cloud storage system; summarizes the key technologies of currently secure cloud storage systems, such as encryption key’s distribution and management, attribute-based encryption, searchable encryption, ciphertext-based data deduplication, provable data possession and proof of retrievability mechanism, data assured delete, etc. At the end of paper we discuss the future research directions of secure cloud storage system.