The research interest in pattern avoiding permutations is inspired by Donald Knuth’s work in stack-sorting. According to Knuth, a permutation can be sorted by passing through a single infinite stack if and only if it avoids a sub-permutation pattern 231. Murphy extended Knuth’s research by using two infinite stacks in series and found out that the basis for generated permutations is infinite but Elder proved that the basis is finite when one of the stack is limited to depth two and the permutations are algebraic. My research is to investigate the permutations generated by a stack of depth 3 and an infinite stack in series. It is to determine the basis and nature of the permutations in term of formal language.