Abstract: Root rot severely restricts the sustainable development of Astragalus membranaceus var. mongholicus (AMM) industry. Resistance breeding is an economical and environmentally safe way to manage the disease and its key lies in the obtaining of resistance indicators. This study aimed to quickly and accurately screen the resistance-related (RR) metabolites so as to provide reference for the screening of indicators of AMM breeding for resistance. LC-MS-based targeted metabolomics and real-time quantitative PCR technology were employed, in combination with multivariate statistical analysis, in analyzing the dynamic changes of phenylpropanoid metabolites in AMM in response to root rot pathogen Fusarium solani (FS) infection and identifying the differential metabolites. The LC-MS method established showed high sensitivity; each metabolite had a good linear relationship (R² ≥ 0.968 9) in the corresponding linear range of the respective standard curve; the recoveries and the relative standard deviations (RSDs) (n = 6) ranged from 70% to 107% and from 1.2% to 9.9%, respectively. Obvious disturbances were observed in the changes of the targeted metabolites in AMM infected by FS. These metabolites, compared with the mock-inoculated (CK) group, showed different up or down regulation with time series. Calycosin-7-O-β-D-glucoside, ononin, calycosin and formononetin were identified as differential metabolites, and they all belong to flavonoids. The first three compounds were significantly negatively correlated (r ≤ -0.97, P < 0.05) with the content of FS in the root of AMM. As potential RR metabolites, they are helpful in obtaining promising resistance indicators for AMM against FS infection.