A system and method for lot priority adjustment. The system includes a database, a calculation unit and an adjustment unit. The database stores at least a committed date for a lot, a throughput rate and a cycle time for respective route operations in a production line, and Work-In-Process (WIP) information of the production line. The calculation unit calculates an x-ratio for the lot on a target route operation according to a current time, the committed date and a remaining cycle time for the lot, calculates a lot weight for the lot according to current loading of a predetermined number of route operations subsequent to the target route operation, and calculates a weighted x-ratio according to the x-ratio and the lot weight. The adjustment unit adjusts a priority for the lot according to the weighted x-ratio.