Against the background of China's Rural Revitalisation Strategy, agricultural livestreaming has become an important link between the production and marketing of agricultural products. Drawing on the stimulus-organism-response (S-O-R) framework, this study examines consumers who watch livestreams supporting farmers. Data were collected from 482 valid questionnaire responses, and confirmatory factor analysis, regression analysis, and bootstrap mediation analysis were used to examine the mechanisms underlying consumers' purchase intentions. The results show that agricultural livestreaming characteristics have a significant positive effect on purchase intention. Perceived value and perceived trust both mediate this relationship, with perceived trust accounting for the stronger indirect effect. These findings suggest that livestreams supporting farmers operate not only through immediate promotional stimulation but also through an ongoing communication process that shapes consumers' evaluations and judgements. The study extends understanding of the psychological mechanisms underlying agricultural livestreaming and provides practical implications for improving content presentation and strengthening consumer trust.