Follow-up observations are necessary to extract the full potential of microlensing events and find more microlensing planets. People usually select high magnification events to follow because of their high sensitivities, and the event selection is based on wide-field surveys. we used to manually track and monitor all the ongoing events to select follow-up targets. However, since the KMTNet stars its operation, there are \(\sim\)200 ongoing (rising) events at the same time at any moment, it becomes difficult for the observer to monitor such a large number of events. So we build a new system, HighMagFinder, which is based on the KMTNet real-time data. This system runs every 3 hours and it can find and alert all the possible high magnification events. During the operation in 2021, the system has zero false negatives for \(A>50\). Based on it, we followed 35 events with 7 planetary events. The system reduced a lot of human work, and it is also friendly to future statistic works.