The invention discloses a semi-automatic construction control system and method for an excavator. The semi-automatic construction control system and method solve the technical problems of low construction efficiency and low construction precision in the operation process of using the excavator for leveling and slope repairing, and the control system comprises a sensor module, a control module, a measuring module and an operating module; and the measuring module inputs measuring data into the control module, and the control module realizes calculation of the elevation, the flatness and the slope by establishing a coordinate system, meanwhile, the sensor module feeds back the condition of the excavator equipment to the control module, engineering design data are manually input into the control module, the control module transmits correction output signals which are fed back to the operating module, and the excavator enters a two-linkage semi-automatic state to complete the construction.The control system and the control method also have the advantages of low technical requirements for an excavator operator, high construction precision, no need for secondary measurement and the like.