A simple model has been developed to study the thermal consequences of ridge subduction. The geological process is modeled as a flat plate moving over a finite line heat source. Effects of plate velocity, ridge length and the oblique angle between ridge and trench axes have been investigated. Calculated result sindicate that the depth of thermal perturbation of a ridge is inversely proportional to plate velocity. Thermal effects will penetrate deeper into a plate for longer ridges if the ridge axis is parallel to the direction of plate motion. However, depth of thermal disturbance is found to be independent of ridge length if ridge axis is normal to plate motion direction.