In this study, we investigate the relationship between the occurrence region of megathrust earthquakes, slow earthquakes such as a long-term slow-slip event and tectonic tremors, and temperature fields and dehydration processes near the plate interface in the subduction zone of the Cocos plate in southern Mexico, including the Guerrero seismic gap. For this purpose, we performed numerical simulations of 3-D thermomechanical subduction modelling with a combination of multiple unknown model parameters. The unknown parameters used are 1) the downdip limit of the high-viscous region within the mantle wedge, which was introduced by considering the non-uniform thickness distribution of the continental crust, and 2) its viscosity, and 3) frictional coefficient which contributes to the amount of frictional heating at the plate interface. The optimal model that best fits the observed Curie point depth distribution was determined among them whose optimal values for the above respective values were determined to be 55 km, 1.0×1028 Pas, and 0.00085, respectively. Comparing the temperature field for the best-fit model with the occurrence region of the interplate seismic events, the interplate temperature near the occurrence region of the megathrust earthquakes, a 2001-2002, 2006, and 2010 long-term slow slip event at a downdip of the Guerrero gap in the range where the amount of slip is 10 cm or more , tectonic tremors within the seaside swarms, and tectonic tremors within the inland swarms are estimated ranging from 200 to 400℃, from 400 to 550℃, from 500 to 600℃, and from 650 to 750℃, respectively. In addition, in and around the Guerrero seismic gap for the megathrust earthquake, where the slab geometry is concave, the plate interface temperature was estimated about 100°C lower than the surrounding area at the same depth in the along-arc direction. Because it is thought that complete stick-slip behavior does not occur in this low-temperature region, and suggests that it is related to the presence of the seismic gap. Comparing estimated dehydration processes near the plate interface with interseismic events suggests that large dehydration from the MORB within the oceanic crust and the ultramafic rock within the mantle wedge were identified near the long-term slow slip event and the tectonic tremor regions, respectively.