Abstract: Objective To create an instrument to determine the mental disorder offenders' competency to stand trial,which is according with the Chinese legal system.Methods Integrating the foreign instruments and the Chinese criminal jurisprudence,and combing the authors' forensic psychiatric experience,the research team created an instrument which was called Competency to stand trial Determining Instrument firstly,then used the instrument in practice,in the end the validity and reliability of the instrument were inspected,and through an diagnostic test,the feasibility of the instrument was evaluated.Results Split-half and homogeneity reliability of the instrument is0.9366and0.9213respectively,the correspondence of the conclusion between the instrument and the expertise is0.704.Except the sensitivity is0.6097,all the other diagnostic index are over0.80.Con-clusion The Competency to stand trial Determining Instrument is feasible.

Key words: competency to strand trial, instrument, mental disorder offenders