The laser-induced heating in a substrate is investigated in the present study. The non-dimensional form of the governing equation on energy conservation for the unsteady laser heating process indicates that the heating process can be characterized only by two dimensionless parameters, i.e. the dimensionless scanning velocity of the laser spot U and the dimensionless absorption depth A. A criterion, U << 1, is derived to scale down the heat transfer process from three dimensions to two dimensions, which is verified by the present numerical simulation. Another criterion, Lambda > 100, is also given to correlate the heat flux model and the heat absorption model by comparing the numerical results obtained by these two models. The numerical simulation reveals an interesting phenomenon, the lag between the times for laser center reaching a point and the corresponding point reaching the maximum temperature. The present study provides insight into the unsteady heat transfer process induced by laser heating. (C) 2016 Elsevier Ltd. All rights reserved.