A mathematical method is proposed to evaluate the delay performance of RF-Mesh-Networks that can realize data classification transmission and ensure real-time data requirements, for deficiency in evaluating and analyzing the delay performance of different types of transmission data when the large-scale wireless advanced measurement instruments are applied in smart distribution grid. Based on the analysis of the WMNs architecture of the smart distribution grid, the functional relationship between the initiation stages of the two consecutive time slots is established using Markov chain modulation techniques. In order to avoid the difficulty of solving high-order differential equations during the process of obtaining steady-state solutions, the solution method based on error iteration to obtain steady-state operating points is proposed, and the detailed solution process is also provided. On the basis of obtaining the steady-state working point, the analytical formula to evaluate the average delay performance of real-time data and non-real-time data for uplink and downlink transmission. To verify the effectiveness of the proposed delay performance evaluation method for WMNs applied in smart distribution grid, the delay performance of real-time and non-real-time data is simulated and tested，where they are set up three different transmission rates. The experimental simulation and test results show that the proposed method can achieve performance evaluation and analysis of transmission delay for different types of communication data in intelligent distribution networks, and can improve the transmission performance of WMNs.