Ground thermal properties are critical for ground source heat pipe (GSHP)systems design and operation.These properties are usually measured in situ with a polyethylene U tube buried in a borehole with the depth of about 100 m.So the model describing the heat transfer between buried U tube and the ground is very important for the in situ  measurement.The solid cylindrical heat source model considers the inner borehole of a vertical buried loop of ground heat exchanger (GHE) as a solid and heat flux is imposed on the borehole wall，so it is more approximate than the hollow cylindrical heat source model which assumes the inner borehole has no mass，and also more approximate than the line source model which regards the buried U tube as a line heat source with a diameter of zero.This paper used the solid cylindrical heat source model，together with the parameter estimation method，to determine ground thermal properties in situ.Application in real GSHP projects indicates that the measured ground thermal properties were credible and can be used for GSHP systems design.