• We work on a generalized ( 2 + 1 )-dimensional dispersive long-wave system. • With the help of symbolic computation, we give rise to four sets of the similarity reductions, each of which leads to a known ordinary differential equation . • Our similarity reductions are in respect of the horizontal velocity and the wave elevation above the undisturbed water surface. • All of our results depend on the constant coefficients in the system. Active researches on the oceanic water waves have been done. As for the nonlinear and dispersive long gravity waves in two horizontal directions on the shallow water of an open sea or a wide channel of finite depth, the paper commented [i.e., Chaos Solitons Fract. 138, 109950 (2020)] has investigated a generalized ( 2 + 1 )-dimensional dispersive long-wave system. In respect of the horizontal velocity and the wave elevation above the undisturbed water surface, with the help of symbolic computation, we give rise to four sets of the similarity reductions, each of which leads to a known ordinary differential equation. All of our results depend on the constant coefficients in the original system.