Network intrusion has the features of randomness and uncertainty, cloud theory

integrates the fuzziness and randomness perfectly. An evaluation model for network risk is

proposed based on the cloud theory. The model monitors the system resources and processes

the achieved data, then the data is input into the cloud controls, the evaluation result is

achieved finally. The experimental results show that the methods can evaluate the network

risk efficiently. It holds the uncertainty of evaluation process and improves the

reliability of the result.