This application discloses a data flow control method and apparatus. The method includes: calculating, by a device when a clock signal arrives, a quantity of transition-minimized differential signaling (TMDS) characters currently stored in a buffer of the device; and outputting, by the device, the TMDS character in the buffer when the quantity of TMDS characters currently stored in the buffer reaches a preset value, or outputting a gap data packet when the quantity of TMDS characters currently stored in the buffer does not reach a preset value, where the preset value is less than or equal to a TMDS character storage capacity of the buffer.