The property that the stream cipher RC4 can generate the same keystream outputs under two different secret keys has been discovered recently. The principle that how the two different keys can achieve a collision is well known by investigating the key scheduling algorithm of RC4. However, how to find those colliding key pairs is a different story, which has been largely remained unexploited. Previous researches have demonstrated that finding colliding key pairs becomes more difficult as the key size decreases. The main contribution of this paper is proposing an efficient searching algorithm which can successfully find 22-byte colliding key pairs, which are by far the shortest colliding key pairs ever found.