Industrial parks are key contributors to localized urban heat intensification, forming sub-industrial heat islands (IHIs) that influence the urban thermal environment. This study investigates the industrial heat island effect (IHIE) in the Guangzhou–Foshan metropolitan area (GFMA), with a generalized additive model (GAM) to explore the influence of park spatial patterns and land cover characteristics, using indicators such as industrial heat island intensity (IHII), industry warming area (IWA), industry warming efficiency (IWE), and industry warming gradient (IWG). The results show that (1) industrial land significantly contributes to industrial heat islands (IHIs), with heat extending up to 200 m into surrounding areas. (2) IHIE intensity varies notably across park types, with each dominated by different factors: manufacturing parks by landscape shape index (LSI); comprehensive parks by impervious surfaces (IWS) and internal building land (IB); and special parks primarily by IB. (3) In most industrial parks, park area (S), IWS, and LSI are the key factors affecting IHIE. As IWS increases, IHIE strengthens, though this trend can be mitigated by expanding park area. Conversely, a higher LSI weakens IHIE. (4) Several variables, including arable land (AL) and water body (WB), exhibited nonlinear or threshold effects, suggesting that IHIE is shaped by complex mechanisms. These findings offer valuable insights for optimizing land use in urban and industrial planning to reduce IHIE and promote sustainable urban development.