The invention provides a mixed direct-current transmission system capable of implementing inverse power output. The mixed direct-current transmission system comprises a current source type current converter on a rectification side and a voltage source type current converter on an inversion side; a positive pole and a negative pole, which correspond to the current source type current converter and the voltage source type current converter, of a direct-current bus are respectively serially connected with pole isolation switches L8 and L9 and pole isolation switches Y8 and Y9; the pole isolation switch L8 is connected with the pole isolation switch Y8 through a direct-current transmission line; the pole isolation switch L9 is connected with the pole isolation switch Y9 through a direct-current transmission line; inverse power output conversion switches L10 and L11 are in parallel connection between the pole isolation switch L8 and the pole isolation switch L9 in a cross manner, so that two ends of the pole isolation switch L8 are respectively connected with one end of the inverse power output conversion switch L10 and one end of the inverse power output conversion switch L11; and two ends of the pole isolation switch L9 are respectively connected with the other end of the inverse power output conversion switch L10 and the other end of the inverse power output conversion switch L11. By the technical scheme, the cost is low, the mixed direct-current transmission system is easy to operate and control, the application field of the mixed direct-current transmission system is expanded, and the flexibility of a running mode of the system is improved.