The downdip limit of seismogenic interfaces inferred from the subduction thermal regime by thermal models has suggested relating to the faulting instability caused by brittle failure regime in various plate convergent systems. However, the featured three-dimensional (3-D) temperature structure especially along the horizontal two-dimensional (2-D) dimension of a subduction zone remains still poorly constrained. To robustly investigate and further map the horizontal distribution of subduction regime and subsequently induced slab dewatering in a decent plate beneath a convergent margin, we construct a regional thermal model that incorporates an up-to-date 3-D slab topography and the MORVEL plate velocity to simulate plate subduction history in Hikurangi. The calculation provides an identified thrust zone featured by remarkable slab dehydration near the Taupo volcanic arc in North Island distributed along the Kapiti, Manawatu, and Raukumara (KMR) region. Average subduction-associated slab dehydration of 0.09 to 0.12 wt%/km is greater than the dehydration in the other portions of descending slab and possibly contributes to an along-arc variation of interplate pore fluid pressure. A large-scale slab dehydration (>0.05 wt%/km) and a high thermal gradient (>4°C/km) are also identified in KMR associated with frequent deep slow slip events (SSEs). Intra-slab dehydration that exceeds 0.2 wt%/km beneath Manawatu near the source region of tectonic tremors suggests an unknown relationship in the genesis of slow earthquakes.