This study is aimed to design the mechanical gascyclone precipitator with an outstanding collection efficiency as one of ways to reduce exhaust gas of small-scale vessels. It estimated fine particles generated from diesel engines which has become one of the biggest environmental issues currently. Specifically, it quantitatively analyzed the flowing process from the cyclone gas exit; a duct via part to the collecting part of Cylindrical lower using DPIV (Digital Particle Image Velocimetry). Since the gas inlet height part became wider the previous theoretical dimensions, internal fluid characteristics of cyclone where the speed of internal swirl had been slow were investigated by temporary streamline of fine particles at 14-20 ㎛. The results showed that collecting efficiency was three times higher than the conical type utilized previously. In addition, this study supplemented imprecision problems from the previous theoretical equation and CFD interpretation with an experimental method. It also provided a basic data to design the cyclone precipitator by size of diesel engines for vessels.