Aiming at the high complexity, poor flexibility and security problem in the traditional cross-domain access under the dynamic heterogeneous network environment, this paper proposed a multi-level security access model that introduced the risk management mechanism, where a dynamic risk threshold is set for each domain and a risk pre-audit is performed on both subject and object of the access. The model compares the number of access, the cumulative access risk values, and the maximum value within the set access period and then stipulates restriction conditions. For low-risk entities that frequently initiate access, a risk advance limit is offered, and further access is allowed in case of non-overdraft risk limit. After the access, the risk threshold of the domain will be adjusted dynamically to make it a certain dynamic adaptability.