There are some faults in the existing role-based delegation models:(1) most of these models can rarely support a fine delegation granularity effectively;(2) the propagation of permissions in them is poorly-controlled.This paper analyzed these problems

and proposed a fine-grained role delegation model based on mapping mechanism (RDBMPM)

which mainly consisted of a vectorizing operator and a measuring operator.Based on these two operators’ concerted computing

the paper introduced the concept of measuring role

which acts as the authorized granularity in the following discussion of delegation constraint mechanism.Finally the significance of the research on RBAC(Role-Based Access Control) delegation model based on mapping mechanism is justified by the simulating of three typical fine-grained delegation models in RDBMPM.