Bicyclic compound as Lp-PLA2 inhibitor as well as preparation method and medical use of bicyclic compound

The invention relates to a bicyclic compound as an Lp-PLA2 inhibitor, and a preparation method and medical use of the bicyclic compound, as well as a medical composition containing the compound. The structure of the bicyclic compound is as shown in a general formula I, wherein definitions of R1, R2, R3, X, Y, Z, Ar and n are as shown in the description and claim. The compound as shown in the general formula I can be used as the Lp-PLA2 inhibitor for preventing and/or treating and/or improving diseases relevant to Lp-PLA2 enzymatic activity.