A dynamitic video storing method and a network security surveillance apparatus are provided. The dynamitic video storing method is suitable for the network security surveillance apparatus and includes the following steps: first, receive a video signal; then, determining whether a connecting status of the network security surveillance apparatus is disconnected, and determining a residual capacity of a storage unit of the network security surveillance apparatus when the connecting status is disconnected, finally, storing the video signal according to a video parameter after the video parameter for the video signal is set according to the residual capacity. The network security surveillance apparatus may include a video capturing unit, a storage unit, and a processing unit and execute the dynamitic video storing method.