The progression of 2D novel, metal trihalides MX3, has been learned Dirac half-metallicity topological spintronic possessions because of their interest that are inherited magnetic processes reflected by 2D metal trihalide. Recently a new approach has been introduced to calculate the degree-based topological indices of chemical compounds, called the M-polynomial. It gives nice and good results of the topological indices of the corresponding chemical compounds. Then one can use these results to correlate the chemical compounds with their chemical properties and bioactivities. The main interest in this article is the computations and comparisons of the general form of M-polynomial of two types of metal trihalides. Then, the general form of obtained M-polynomials is used to determine the degree-based topological indices of these metal trihalides. In the end, graphical comparisons of the M-polynomial and the topological indices of the metal trihalides are described. Mainly, a comparison among the degree-based indices of metal trihalides is performed with the help of 2D-chart plots and numerical tables.