Abstract: Expressions for the equivalent capacitance of the detecting electrodes in the process of encounterance with a target , and its rate of change versus the distance between the projectile and the target , are derived . For three different kinds of working modes of the detector , i . e ., when projectile body is (1) used as an electrode , (2) not connected to circuit , (3) grounded , theoretical analyses and performance comparisons of the characteristics of the detector' s dynamic target signal are carried out .Through the theoretical analysis of the expression ,the design principle of the electrodes aimed at improvements in the sensitivity of the detector is discussed . Furthermore , characteristic curves of the dynamic target signal are analysed .