The present disclosure provides a data driving circuit and a driving method thereof, a data driving system and a display device. In an embodiment of a data driving circuit, each digital to analog conversion unit is only used for driving sub-pixels of one color, and by controlling on-off of the switch unit, one data line interface unit is enabled to be connected to different digital to analog conversion units when driving sub-pixels of different colors. In this way, a reference voltage can be provided to the digital to analog conversion unit for driving different color display by a single physical Gamma circuit, without having to use a digital Gamma circuit. Therefore, gray scale loss caused by adjustment using the digital Gamma circuit can be avoided fundamentally.