The tragedy took place in Nongzhuang Village in Kaixian County on Monday when Yang Guohai, 29, murdered his girlfriend, her parents, her elder sister and her sister's child.
According to relatives and neighbours, Yang had argued with the family over marriage on Saturday.
The police said Yang called his mother on the morning of the crime and claimed he would "perish with the Yan family."
Yang's body was found in a pond not far from the crime scene today, state-run Xinhua news agency reported.