Graded-index multimode fiber (GI-MMF) is advantageous for low modal dispersion over its counterpart step-index multimode fiber, which renders it highly suitable for high-speed data transmission in short-range data links. To date, several theories and calculation methods have been proposed for MMF transmission and connection, most of which are based on geometric optics. Although the basic principle is extremely simple, the manipulation of the modal power distribution (MPD) variation along the transmission line that considerably affects the channel bandwidth still poses several challenges. Currently, the radiance of a point on the emitting fiber is assumed to evaluate the MPD at fiber connections, as its measurement or calculation method has not been determined yet. Thus, this paper proposes a method to numerically estimate the point radiance of GI-MMF using the near-field pattern (NFP) and far-field pattern (FFP) of the fiber. The method used data based on analytic functions representing NFP and FFP and yielded accurate estimations for the point radiance of GI-MMF; the accuracy was verified by comparing the fiber NFP and FFP calculated from the derived point radiance with the NFP and FFP analytical functions. In addition, the numerical aperture of the points on the fiber end-face obtained from the point radiance was in accordance with the theoretical value. Subsequently, we substituted the point radiance function of the GI-MMF into the matrix model that was established to compute the MPD conversion at fiber connectors under generic misalignments, including lateral, longitudinal, and angular offsets. Accordingly, the influence of misalignments on the MPD in GI-MMF connectors was assessed, and the performance of the fiber channel linked by GI-MMF was evaluated.