The invention belongs to the field of internet CDNs (Content Delivery Networks), and discloses a system and a method for supporting HTTPS (Hyper Text Transfer Protocol Security) by a high-availabilitysecure private-key-free CDN, and the system comprises a TLS (Transport Layer Security) handshake agent device, a query agent device and a private key management device. A CDN node where the TLS handshake agent device is located does not store a private key of a website, but sends data to a private key management device of the website when the device needs to be used, the private key management device processes the data and then returns the data to the CDN, and the CDN carries out subsequent processing. Wherein the query agent devices are provided with cache queues, the number of the query agent devices is two, and the number of the private key management devices is multiple. According to the invention, the CDN supports HTTPS, and the private key does not need to be deployed on the CDN, sothat the absolute private control of the private key owner on the private key is kept, and the security is improved. Meanwhile, the device in the system has high availability, and the optimal line can be automatically selected according to the private key management device equipment load and the network condition.