The invention discloses a method for calling video communication service by video communication terminal. The method comprises the steps of: (a) a first video communication terminal launches a call to a multipoint control unit (MCU) and sends an conference information needed for convening a conference to the MCU through an In-Band channel established between both sides; (b) the MCU convenes the conference according to the conference information received. The invention also discloses a message data form for transferring information through an In-Band channel in a video communication service. The message data form comprises: a data starting mark field, a data type field, a data length field, a field for no less than one piece of sub-information, a data ending mark field and a cyclic redundancy check field.