To reveal the effect of temperature on the passivation of phosphorus (P) and arsenic (As) at the sediment-water interface (SWI) by the La-modified bentonite (LMB) and identify the optimal temperature, surface sediments from a eutrophic shallow lake was used as the research object. Laboratory simulation experiments were conducted using techniques such as a microelectrode system, high-resolution pore water sampling technology, and inductively coupled plasma-Mass Spectrometry (ICP-MS). The distribution characteristics of dissolved oxygen (DO), pH, iron (Fe), manganese (Mn), and dissolved organic matter (DOM) at the SWI under different temperatures (10℃, 20℃, 30℃) were analyzed, and the occurrence patterns of dissolved P and As were identified with high precision. The results showed that: Increased temperature leads to a decrease in DO concentration, an increase in pH, and a rise in DOM content at the SWI. The formation of an anaerobic environment promotes the reductive dissolution of iron-manganese oxides, resulting in the release of dissolved P and As; The optimal temperature for the immobilization effect of LMB coverage on dissolved P and As was 20℃. On the 7th day, the concentrations of dissolved P and As at the SWI under LMB coverage decreased by 86.36% and 38.61%, respectively, and by 86.15% and 12.57% on the 50th day. The addition of LMB transformed mobile P and As in sediments into stable forms: at 20℃, the proportion of stable P in sediments increased from 48.95% to 51.45%, and stable As increased from 51.68% to 60.39%. The study confirms that the passivation effect of LMB on dissolved P and As at the SWI is temperature-dependent. The research results can be applied to the control of internal pollution in shallow lakes in temperate and subtropical regions during summer and autumn.