To provide a performance prediction program and a performance prediction system for a ground source heat pump system which can be applied to system design by calculating a predicted underground temperature for the ground source heat pump system with high accuracy and predicting the performance of the ground source heat pump system based on the resulting underground temperature changes, etc., considering the use of a plurality of buried tubes, underground temperature changes for buried tubes placed at different intervals, and the use of a U-shaped tube heat exchanger.

This program makes a computer function as a dimensionless distance calculating means 311 calculating a dimensionless distance, a first dimensionless time calculating means 312 calculating a first dimensionless time that is the boundary between a zero area and a linearly increasing area, a second dimensionless time calculating means 313 calculating a second dimensionless time that is the boundary between a diagonal increase area and the linearly increasing area, a boundary time acquiring means 314 acquiring a first boundary time and a second boundary time, an underground temperature change calculating means 315 calculating underground temperature changes, and a tube surface temperature change calculating means 316 calculating underground temperature changes on the buried tube surfaces.