Experimental investigation of parametric coupling of two vibration modes in a two-coupled-cantilever-based mechanical system is carried out, and the influence of mode frequency difference on coupling strength is investigated. In the experiment, a tunable two-mode system is constructed by trapping one of the cantilevers optically, and the parametric coupling between the two modes is realized by applying a parametric drive through periodically modulating the trapping power. Furthermore, the parametric coupling under distinct frequency differences between two modes is studied and the relationship between coupling strength and frequency difference is obtained experimentally. The result is beneficial to realizing the accuracy control of the coupling strength of two modes under distinct frequency differences.