  We make a systematic calculation on $\alpha$-decay branching ratios to
members of ground-state rotational band and to excited $0^{+}$ states of
even-even nuclei by a simple barrier penetration approach. The branching ratios
to the excited states of daughter nucleus are determined by the $\alpha$-decay
energy, the angular momentum of $\alpha$-particle, and the excitation
probability of the daughter nucleus. Our calculation covers isotopic chains
from Hg to Fm in the mass regions 180$<$A$<$202 and A$\geq$224. The calculated
branching ratios of $\alpha$-transitions are consistent with the experimental
data. Some useful predictions are made for future experiments.
