  By a well-known theorem of Thomassen and a planar graph depicted by Voigt, we
know that every planar graph is $5$-choosable, and the bound is tight. In 1999,
Lam, Xu and Liu reduced $5$ to $4$ on $C_4$-free planar graphs. In the paper,
by applying the famous Combinatorial Nullstellensatz, we design an effective
algorithm to deal with list coloring problems. At the same time, we prove that
a planar graph $G$ is $4$-choosable if any two $4$-cycles having distance at
least $5$ in $G$, which extends the result of Lam et al.
