In this paper, we have studied the nonlinear interaction of two cascade three-level atoms with single 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-organization may occur in many-atom system to form a "large atom system" at the thre-shold, producing synchronous ordered emission Meanwhile, the second-order correlation degree of two-atom system is larger 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 stren-gth of exciting field is reguired to be also stronger.