The sand play technique (Sandspiel) has often been used in psychological treatments. The primary purpose of this study was to construct a practical virtual environment to support the application of this technique with computers. The prototype application called “Virtual Sand Box” was developed to test the Sand Play Technique in the diagnosis and treatment of autistic patients. The display system and input device are discussed. A detailed description is also provided for how a virtual environment was constructed to cater input systems into output systems in order to facilitate manipulation tasks for the user. Experimental results gave insight into the feasibility and advantages of applying virtual reality technology to clinical medicine, particularly with respect to the diagnosis of the people with psychological and psychiatric sicknesses such as autism and neurosis.