The traditional preparation process of sebacic acid by cracking castor oil was studied and the reason of producing a large number of waste water containing salt and phenol was analyzed.a new technological process and new condition for preparing sebacic acid by one step acidification method was put forward and the effect of water dosage on yield of products was investigated.The results indicated that sebacic acid yield of the new process is the same as that of the original process,and the quality of products was in accord with the national standards,however the wastewater quantity was only about 1/4of traditional method.It create conditions for pollution treatment of preparation of sebacic acid completely.