Private desktop cloud is widely used in various kinds of application scenarios, such as centralized computing, centralized management, and remote office. Existing private clouds are mostly based on OpenStack operating system, however, OpenStack encounters a problem that it takes a long time to start a virtual machine when it is used in private desktop cloud, so it is unable to meet the real-time requirement in some application scenarios. In this paper, using template image strategy and network attached storage strategy for the cloud storage layer, Instant-Start Virtual Machine (ISVM) private desktop cloud architecture was proposed. ISVM private desktop cloud architecture consisted of cloud management layer, cloud storage layer, and cloud service layer. Through testing and analyzing, the time of starting virtual machines in ISVM architecture is about one percent of the time in OpenStack architecture, reaching millisecond order of magnitude and meeting the real-time requirement of some application scenarios.