Merging unit is the key device in the process layer network of smart substation, and the stability of the operation of merging unit is very important for the reliable operation of smart substation. In order to eliminate the impact of network storm on merging unit in the data cascade, this paper proposes a real-time filtering method for cascade network storm. Based on the analysis of the characteristics of the cascade storm packet, the filtering method of hardware filter and software filter is proposed to suppress merging unit cascade network storm. In the terms of hardware filter, the storm packet flowing in is effectively controlled in real time by the multiple filter and flow control unit. In the terms of software filter, storm packet is effectively filtered by the multi-filter algorithm based on IEC 61850-9-2 packet characteristics. The method is tested through the network storm test platform, the reliability of the method is validated, and the stability and reliability of merging unit in smart substation are improved.