Abstract: In the radioactive measurement of environment sample with HPGe detector, it is evident that the higher detection efficiency, the less measurement time and the more spectrometer’s utilization. For the same sample volume, the shape of environment sample may affect the detection efficiency. The detection efficiency of environment samples which filled in different shapes for saddle-like sample boxes with the same volume was simulated with MCNP code, and the optimum shape was found and demonstrated by experiments. Results of both experiments and simulations show that the detection efficiency of the optimum shape for saddle-like sample box is twice higher than that of cylinder sample.