A femto cell connection node, a femto cell system, and a data transmission method of the system are disclosed.In the case where a sending terminal is willing to transmit data to a receiving terminal, a femto cell connection node of the sending side determines a present connection state of the receiving terminal and determines a transmission format of the data to be transmitted from the sending terminal to the receiving terminal according to the determined connection state. In particular, in the present disclosure, in the case where the receiving terminal is in a state of being directly or indirectly connectable to an Internet Protocol (IP) network, the data is transmitted to the receiving terminal after changing a protocol portion L1/L2 so that the data may pass through the IP network.