Abstract: The NNR(No-Net-Rotation)-MORVEL(Mid-Ocean Ridge VELocity) 56 is a set of angular velocities describing the motions of 56 plates relative to a No-Net-Rotation reference frame.These plates can be adjusted in terms of non-overlapping polygonal regions,separated by plate boundaries on a unit sphere.During the calculation on the kinematic parameters for these 56 plates in a NNR reference frame using the International Terrestrial Reference Frame(ITRF) velocity field,the geometric parameters of tectonic plates play a significant role in establishing an absolute plate motion model based on space geodesy results.The computational method for these geometric parameters implemented as a FORTRAN90 program is described in this paper,allowing an evaluation of the area and the inertia tensor of a polygonal region on a unit sphere.This program is mainly built on a triangulation algorithm and the adaptive Simpson's double integral method for spherical polygons,which produces highly reliable results for all 56 modern plates.