On the basis of charm scheme for subhadronic constituents (p, n, λ, p′), we have studied the weak decay processes. The total decay probability and the semi-leptonic decay probability are semi-empirically estimated by using the existent experimental data. From this analysis, we conclude that the non-leptonic decay of charmed meson is not sharply enhanced in contrast to the case of ordinary strange hadron decays. Some related problems are also discussed for symmetry arguments especially on the sum rules based on the general property from iso-spin and SU(3) symmetries.