Building visible intercom system connection method, password setting method and system

The invention provides a building visible intercom system connection method. An outdoor unit machine transmits a call request to a cloud-side server; the cloud-side server detects operation of the intercom programs of user terminals, and the call request is transmitted to the user terminals if the intercom programs of user terminals operate; or a VOIP business starting instruction is transmitted to the outdoor unit machine; and the outdoor unit machine transmits the call request to the user terminals via a PSTN network, and the user terminals establish corresponding connection with the outdoor unit machine according to the format of the call request. The invention also provides a password setting method. The user terminals transmit passwords to the cloud-side server and then the cloud-side server transmits the passwords to the outdoor unit machine. The invention further provides a building visible intercom system. The system comprises the user terminals, the outdoor unit machine and the cloud-side server. The user terminals substitute a conventional indoor machine so that the networking structure is simple, the used communication equipment is less and maintenance quantity is low. Networking of the unit machines and the user terminals can be realized via a data communication network and the PSTN network so that the regional restriction of use of the conventional building intercom indoor machine can be avoided.