The invention relates to a cloud service accessing gateway system and a cloud service accessing method. The cloud service accessing gateway system comprises a client side, a cloud service accessing gateway and a cloud resource server. The cloud service accessing gateway comprises three functional layers including a user interaction layer, a safety certification layer and a single sign-on layer. According to requirements on security and management of the cloud service accessing gateway system, frequent data transmission and synchronous information processing are performed among the cloud service accessing gateway, the client side and the cloud resource server, so that coordination action of cryptographic authentication and single sign-on is realized. The cloud service accessing method includes: a user of the client side logins in the cloud service accessing gateway system to get login authentication via conversation initializing units like request interaction, resolution, message audit and resource authorization; the user logins in the cloud service accessing gateway to request a cloud service; and the user logins in the cloud service accessing gateway for cloud service migration. Via forms of one-time registration, one-time login-in and multiple times of accessing, procedures for the user to use the cloud service are simplified, and great convenient conditions are provided to management of cloud resources.