The synchronization factor is a measurement for the consistency of actions between individuals in a jumping crowd，as well as a key metric in the modeling of crowd jumping loads. Most of the existing synchronization factors are defined as mean parameters during a long period of time，and thus cannot accurately reflect the time-varying characteristics of individual differences between jumpers. Their calculation is based on ground reaction force or feature point trajectory records that can only be obtained under laboratory conditions，making it difficult to apply them to the safety operation and maintenance of the engineering structures in actual scenarios directly. In this regard，this paper proposes a new time-varying synchronization factor for crowd-jumping loads. By introducing multiple objects tracking technology to monitor the real-time synchronization variation of the subject jumping processes as the basis for the factor calculation，this study carries out a multi-person jumping experiment with a wireless force measurement shoe pad. By comparing with the test results，the validity of the proposed time-varying synchronization factor and the effectiveness of the multi object tracking technology are verified. The results can be used for the intelligent operation and maintenance of the engineering structure，as well as the simulation of the time-varying crowd jumping loads.