警方鉴定人应当出庭作证的理论基础是各国刑事诉讼所普遍遵循的直接言词原则。警方鉴定人出庭作证可以使鉴定结论的证明力得到检验,还可以促进鉴定人鉴识水平的提高。警方鉴定人出庭作证时应当遵循法定的程序内容,掌握出庭作证的基本原则技巧,特别是应当重视出庭作证的心理调适。 The rationale that police appraisers should appear in court to testify is the principle of direct verbalism generally followed by criminal proceedings in various countries. The testimony of the police appraiser in court can test the testimony of the appraisal conclusion and can also promote the appraising of the appraiser. The police appraiser should follow the statutory procedures when attending court to testify, master the basic principles and techniques of attending court testimony, and in particular, should pay due attention to the psychological adjustment of attending court testimony.