An excavation control system includes a working unit, hydraulic cylinders, a prospective speed obtaining part, a relative speed obtaining part, a speed limit selecting part and a hydraulic cylinder controlling part. The prospective speed obtaining part obtains first and second prospective speeds depending on first and second intervals between first and second monitoring points of the bucket and a designed surface, respectively. The relative speed obtaining part obtains first and second relative speeds of the first and second monitoring points relative to the designed surface, respectively. The speed limit selecting part selects one of the first and second prospective speeds as a speed limit based on relative relations between the first and second relative speeds and the first and second prospective speeds, respectively. The hydraulic cylinder controlling part limits a relative speed of one of the first and second monitoring points to the speed limit.