The present invention discloses a method and system for transmitting a transmission block in a downlink control channel. The method comprises the steps that: a base station selects an idle cell radio network temporary indicator and configures the idle cell radio network temporary indicator to a terminal as TBC-RNTI; the base station compares a transmission block to be sent and a preset threshold; if the transmission block size is not larger than a threshold value, the transmission block is configured into downlink control information (DCI) according to a predetermined rule, a transmission block mapping DCI (TB-DCI) is formed, a CRC cyclic check code is generated, and a TBC-RNTI is used to carry out the scrambling of the cyclic check code; the check codes of TB-DCI and TBC-RNTI scrambling are subjected to encoded modulation mapping to a physical downlink control channel (PDCCH) according to a present technical DCI processing mode; the terminal receives and decodes the PDCCH, and if the TBC-RNTI is detected, the decoded data forms a transmission block according to a predetermined rule, and the transmission block is submitted to an upper layer. The PDCCH detection ability of the terminal is effectively utilized, and the resource utilization rate of the system is improved.