Abstract: To explore the anomaly of conductivity and diffusion coefficient of probe ions in monohydroxy alcohols, molecular dynamics simulation method is employed to study microscopic structure and diffusion coefficient of 2-pentanol with relatively simple structure and lithium chloride is mixed into the system to provide probe ions. The simulation results show that the diffusion coefficient of probe ions in 2-pentanol exhibits anomaly: increasing first and then decreasing with raising temperature, consistent with the previous experimental results; however, the diffusion coefficient of 2-pentanol molecules shows a monotonically increasing trend with raising temperature. Further analysis indicates that there are obvious hydrogen bond molecular clusters in 2-pentanol, and the average molecular number and the average size of the hydrogen bond molecular clusters, the average probability of molecular forming hydrogen bond and the volume of the system all show a crossover. Based on the variation characteristics of hydrogen bond molecular clusters with temperature, the reasons for the anomaly of the diffusion coefficient of probe ions is revealed according to the microscopic mechanism of diffusion coefficient, which are the shortening of ion movement channels caused by the reducing of hydrogen bond molecular chains and the faster and faster increase of molecules not forming hydrogen bond when temperature goes up. This viewpoint can also provide a reasonable explanation for the monotonic increase of the diffusion coefficient of 2-pentanol molecules with raising temperature. The research in this paper not only discovers the reason for the anomaly of diffusion coefficient of probe ions in 2-pentanol, but also indicates that some macroscopic and microscopic quantities of 2-pentanol also have crossover around the temperature of diffusion coefficient anomaly of probe ions.