Robust sensor system plays an important role in Internet of Things (IoTs). These intelligent sensors are required to be low cost and reliable, which provides confidentiality for private sensitive data. However, this protected system is still under the risk of Differential Fault Analysis (DFA) attacks. In this paper, we focus on DFA attacks to AES decryption as decryption receives the equalling importance as encryption. First, we induce a fault at the input of the third round in the procedure of AES decryption, in which w e successfully break it using one pair of fault-free and faulty plaintexts within 232 searching space. Then, we improve this attack by use of S-Box distribution table, which reduces the computational time from 853 ms to 70 ms on a dual Intel(R) Pentium(R) E6700 core (3.20 GHz). Compared to the existing work, our proposed attack reduces 79.5% computational time when both methods employ two pairs of fault-free and faulty ciphertexts/plaintexts.