Late blight (Phytophthora infestans) severely reduces potato production in semiarid Inner Mongolia, and intensive chemical control presents ecological risks. In this study, an ecological strategy for sustainable potato production was developed using a potato-common vetch intercropping system with reduced irrigation and phosphorus redistribution. Phosphorus redistribution could promote common vetch biological nitrogen fixation and growth, thereby strengthen its ecological service capacity. A two-year field experiment demonstrated that intercropping improved tuber yield (by 3.57-22.96%) and comprehensive quality (by 77.80%-307.57%), and reduced late blight (by 23.84%-42.60%). Intercropping under reduced irrigation and phosphorus redistribution yielded comparably to that under conventional irrigation with phosphorus redistribution, reducing the disease index by 42.3% relative to monoculture. Potato yield was positively associated with soil water content and available phosphorus. Quality was correlated with soil total carbon, total potassium, and available phosphorus, and the disease index exhibited a negative correlation with soil available phosphorus and nitrate nitrogen. Intercropping enriched 15 disease-suppressive taxa and shifted fungal community assembly from deterministic to stochastic processes, with fungi contributed most to disease suppression (11.3%). Fifteen disease-suppressive metabolites were also enhanced under intercropping, particularly when phosphorus was redistributed. Agar plate inhibition assays confirmed the inhibitory effects of 2-furancarboxaldehyde, imidazole-4-acetaldehyde, and methyl jasmonate on pathogen growth. Variance partitioning analysis identified disease-resistant metabolites as the key driver (17.2%). Common vetch growth coordinated soil nutrients, disease-resistant microbiota, and metabolites to suppress late blight. Phosphorus redistribution improved yield and quality while reducing disease under reduced irrigation, supporting potato production with lower water and chemical inputs.