The aim of this study is to understand how the interfacial pressure between two dielectric plates of epoxy resin affects the partial discharge (PD) characteristics in the fissure voids in epoxy resin. The specimen consists of two epoxy resin plates keeping needle-plate electrodes and an interfacial fissure-like void at the interface. This is subjected to the mechanical pressure to investigate the effect of interfacial pressure on PD characteristics. The PD characteristics were measured with both a conventional pulse method and a Lissajous' figure method using the computer aided partial discharge analyzing system (CAPDAS). The swarming pulsive micro discharge (SPMD) ratio was introduced by using the two different detection methods. The experimental results in our tests shows that the interfacial pressure does not affect the PD inception voltage and extinction voltage in the specimen with needle-plate electrodes. On the other hand, by increasing the interfacial pressure, the charge of negative PD pulse became smaller and the SPMD ratio for positive PD increased remarkably.