Embodiments of this application provide a method applied to a signal synchronization system, a system, a stylus, and an electronic device. The system includes a stylus and an electronic device. The electronic device supports a first refresh rate and a second refresh rate. The method includes: after an electronic device is wirelessly connected to a stylus, the electronic device samples a downlink signal from the stylus based on a third refresh rate, where the third refresh rate is equal to a first refresh rate or a second refresh rate; and the stylus sends the downlink signal to the electronic device based on the third refresh rate, and samples an uplink signal from the electronic device at a fourth refresh rate, where the fourth refresh rate is the least common multiple of the first refresh rate and the second refresh rate. In the embodiments of this application, after the stylus is connected to the electronic device, the uplink signal from the electronic device may be monitored by using the least common multiple of all refresh rates supported by the electronic device, so that the switching of the refresh rate of the electronic device can be detected in a timely manner, thereby achieving a small time delay and high efficiency.