The Purpose: based on the personnel assessment theory, this study puts up the general procedure of controlled leaderless group discussion and explores its efficiency. The method: the study has the within subject design, every group participates both the controlled and uncontrolled leaderless group discussions. The resuls: the scorer consistency reliability of controlled leaderless group discussion is better on the six qualities such as the organizational coordination ability, language competence, analytic and judging capacity, team cooperation ability, initiative and confidence; The score validity of controlled leaderless group discussion is better on the four qualities such as the organizational coordination ability, analytic and judging capacity, team cooperation ability and confidence; The controlled leaderless group discussion induces the participants to expose more observation points by affecting the group atmosphere(the intense degree of the group and the conflict of the group); The conclusion:Controlled leadership group discussion could induce the participants to expose more observation points, with the result of increasing the reliability and validty of the assessment