With the wide application of Industrial Control Systems (ICS) and the continuous increase of networking, the security threats faced by ICS are increasing. In this context, the security assessment of ICS has become a crucial part of subsequent defense work. However, most of the existing studies on the assessment of ICS use the traditional affiliation functions, which pinpoint problems when dealing with fuzzy phenomena and fail to fully reflect the uncertainty in the assessment process. In order to effectively deal with the ambiguity and randomness problems in the assessment process of ICS, this paper introduces the cloud model theory into the security assessment of ICS. The overall assessment of the security of the ICS system is obtained by using the cloud generator algorithm in the cloud model in combination with known weight calculations. Finally experimental results show that the evaluation results are consistent with the actual situation, and verify the validity and reasonableness of the proposed method.