The invention discloses a day-ahead optimal scheduling method for an AC and DC power distribution network based on a power electronic transformer. The method comprises steps that firstly, a mathematical model for optimizing operation of the PET-based AC and DC hybrid power distribution network is established, the mathematical model for optimizing operation of the PET-based AC and DC hybrid power distribution network is solved, for the mathematical model, total loss of the AC and DC hybrid power distribution network is minimized, the minimum sum of line loss and PET loss is taken as an objective function, and the AC/DC power grid power flow constraint, the PET steady-state operation constraint, the system safety operation constraint, the distributed power supply operation constraint, the energy storage device operation constraint and the AC power distribution network three-phase voltage imbalance constraint are taken as constraint conditions. The method is advantaged in that the flexible regulation and control capability of the power electronic transformer of the AC and DC power distribution network power flow and influence on economic improvement of the AC and DC power distributionnetwork are fully excavated, uncertainty of distributed power supply output and uncertainty of load fluctuation are considered, conservative property and economic property are considered, and the node voltage out-of-limit and line power out-of-limit risk can be reduced.