The paper addresses on the survey and research of tulous and clan ancestral temples at three Hakka hamlets located at the northern part of Zao-an County, Zhangzhou City, Fujian Province, which are Longtan-Lo Hamlet in Chenlong Village, Xiuzhuan Township, Dalou Hamlet in Dabien Village, Guanpi Township, and Suichang-lo Hamlet in Suisha Village, Xiage Township. The paper adopts ""phenomena-hypothesis-verification"" as research method. Five phenomena about tulous and clan ancestral temples had been found in previous field surveys. According to the five phenomena three hypotheses are proposed as follows. 1) Tulou initiated a hamlet. 2) The solidarity of clan, the immigrants of other clans, or substitute of building types might cause the development or divergence of a hamlet. 3) The place of a clan ancestral temple indicates the importance of tulous in a hamlet. After that, literature review, field survey, and map analysis are executed to verify three hypotheses. This research has four findings. 1) A hamlet was named after a tulou does not mean the hamlet emerged from the tulou. That only means that the tulou is significant enough to be an indicators of the hamlet. 2) The development of tulou cluster can be categorized as three patterns: expansion, clone, and scatter, relating to the solidarity of clan, and substitute of building types. Clan development and increase of population causes main tulou expand its accompanying tulous. When space is insufficient, living environment is not satisfied, and building is too old to be maintained, the householders move out and live in surrounding new scattered houses. The remote cause is that the clan solidity had been weakened after the Cultural Revolution. The proximate cause of hamlet deconstruction is the economic improvement after the Reform of China. 3) The evolution of clan ancestral temple-tulou relationship is from ""a unit of tulou"", ""an isolated temple in tulou"" to ""an isolated temple outside tulou"", and ""a unified family temple"". 4) The importance of tulous in clan as well as hamlet is declining. It can be sensed from the phenomena of the idle and dump of tulous, the scattered new houses surrounding old tulous, and the typological evolution of clan ancestral temples.