In this paper, we have studied the nonlinear interaction of two cascade three-level atoms with singe mode field. The results show that the cooperative emission of two atoms can translate into synchronous when the strength of exciting field reaches a certain threshold. That is self-oganization may occur in many-atom system to form a “large atom system” at the threshold, producing synchronous ordered emission. Meanwhile, the second-order correlation degree of two-atom system is lager than that of single atom system due to the synchronous emission effect, i.e.bunching is strong but antibunching is weak. Moreover, the deeper squeezing of two-atom system is obtained since many-photon processes become stronger, and the strength of exciting field is required to be also stronger.