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Studies have shown that temperature is closely related to human metabolism, but only a few studies have focused on the effect of abmient temperature on gestational diabetes mellitus (GDM). Evidence from temperate regions is particularly lacking. Our study aimed to explore the association between ambient temperature during pregnancy and the risk of GDM, and further analyze the critical window. This study used data from the Shandong Multi-Center Healthcare Big Data Platform (SMCHBDP). Generalized additive model (GAM) and logistic regression were used to analyze the association between ambient temperature and the risk of GDM. Distributed lag non-linear models (DLNMs) were applied to assess the critical window. Among 3052 subjects, 382 pregnant women were diagnosed with GDM (12.52%). GAM and logistic regression showed that high mean temperature (> 25.18℃) during the 2nd trimester was the risk factor for GDM, and the aOR (95%CI) was 1.67 (1.15-2.45). Extreme high temperature during 13th-18th weeks of gestation was associated with an increased risk of GDM. The effect was greatest at the 16th week of gestation, and the ORs for maximum temperature, minimum temperature and mean temperature were 2.15 (1.19-3.89), 2.25 (1.27-4.01) and 2.71 (1.43-5.13), respectively. An increased risk of GDM was observed for each IQR (2.2 °C) increase in diurnal temperature range (DTR) at 17th-21st weeks of gestation. Therefore, extreme high temperature and DTR affect GDM mainly in the 2nd trimester. These findings highlight the need for targeted protective measures for pregnant women during these periods, especially amid global warming, to mitigate temperature-related GDM risk.