Avionics Full Duplex Switched Ethernet ( AFDX ) standardized as ARINC 664 is an upgrade from Ethernet for avionics demand .AFDX adopts the mechanisms such as Virtual Link ( VL) and traffic policing for the determinacy of communication task .Network calculus approach is a basic tool to compute the upper bound of end-to-end delay for VL in AFDX network,which give AFDX a useful method to research the real-time performance .However,the network calculus approach used a simple flow model of VL .Based on that model,the result got by network calculus approach is pessimistic .An accurate flow model of VL is adopted in the network calculus approach in this paper,and it helps the network calculus approach to get a tighter upper bound of delay for VL .%航空电子全双工交换式以太网（ AFDX）是针对航空电子应用从工业交换式以太网升级而来的。其中，引入的虚拟链路（ VL）和流量管制机制为网络通信任务提供了确定性的保障。网络演算是AFDX中常用的VL延时上界计算工具，为AFDX网络的实时性研究提供了理论依据。但是网络演算采用了VL简单流模型，计算得到的延时上界比较悲观。将VL精确流模型应用在网络演算工具中，并展示了基于精确流模型的网络演算能够得到更紧的延时上界计算结果。
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