As an open-source distributed programming framework, Hadoop has gradually become popular in industry recently. Its Hadoop Distributed File System (HDFS) enables storing large data with advantages of high fault tolerance and throughput. However, the fact that the current HDFS does not support intra-cloud data encryption yet makes data privacy becomes a key security issue. This paper presents a hybrid encryption method based on HDFS. The authors adopt symmetric encryption to encrypt and decrypt file blocks at data-nodes and use asymmetric encryption scheme to protect the symmetric keys.