A controller is configured to determine a target excavation depth of a first pass based on a position of an excavation end, a target soil amount, and an excavation distance. The controller is configured to move a work implement to the target excavation depth of the first pass to execute an excavation of the first pass. The controller is configured to acquire an actual soil amount excavated in the first pass. The controller is configured to modify the target soil amount based on the actual soil amount. The controller is configured to determine the target excavation depth of a second pass based on the modified target soil amount. The controller is configured to move the work implement to the target excavation depth of the second pass to execute the excavation of the second pass.