The security of block cipher Zodiac against impossible differential cryptanalysis was re-evaluated. By analyzing the properties of diffusion layer P, two new 14-round impossible differentials of Zodiac were introduced. Based on the new impossible differential characteristics and combining with the Early-Abort technique, an effective attack was applied to the full 16-round Zodiac, and the data complexity was 285.6 chosen plaintexts and the time complexity is only 232.6 encryptions. Compared with the previous best result, the time complexity in this paper decreases with a factor of 233. The result shows that Zodiac is vulnerable to impossible differential cryptanalysis due to its poor diffusion.