The invention discloses a time synchronization mechanism of an ultrasonic stereotactic positioning system based on a wireless sensor network, which belongs to the technical field of wireless stereotactic positioning. With the adoption of the time synchronization mechanism, the problem of time synchronization in wireless ultrasonic stereotactic positioning is solved on basis of a wireless sensor network technology and by utilizing four-way handshake communication between a goal node and a reference node, solves, so that global network nodes keep an identical time reference, high positioning accuracy and instantaneity on the goal node are high, and the problems that wiring in an ultrasonic stereotactic positioning system is complex in the wired mode, the positioning accuracy is poor because the network node clocks are not synchronous in the wireless mode and the like are solved. The time synchronization mechanism has a wide applicable scope and high expandability, and can be used for solving the problem of time synchronization in different wireless stereotactic positioning systems.