Aiming at the threats in the process of data aggregation, a secure data aggregation mechanism based on multi-routing transmission for wireless sensor networks is proposed. The data is divided into different dimensions before transmission, and then the divided data are transmitted by means of multi-routing. Meanwhile, the encrypted data do not need to be decrypted in the process of data transmission. The security of the new mechanism is analysed from the aspects of external attacks and insidious attacks. Analysis results show that the wireless sensor networks by means of the new mechanism can effectively protect against eavesdropping, routing packet discarding and data packet discarding.