The purpose of this work is to acquire the flow field distribution characteristics in the liquid-liquid gravity separator at different geometric dimensions. The flow flield structure of initial incoming fluid needs to be rectified in order to make the fluid more uniform and stable before entering the separation zone of liquid-liquid gravity separator. The flat impingement baffle is improved to the entire height rectangular baffle. A numerical simulation based on the volume of fluid (VOF) method was executed using Ansys Fluent 16.2 to analyze the characteristic of flow flield structure of impacted area caused by rectaugular section. The relative unevenness (Mf) and mean turbulence intensity (Iave) were used to investigate the effect of geometric dimensions in the separator, i.e., the effect of inlet diameter of the nozzle (d), length of the impingement baffle to the inlet (lb) and width of the baffle plate (w0). The results of research showed when relative unevenness and mean turbulence intensity were considered together, the separation of two phase was more favorable with the range of the inlet diameter (d/w) equal or greater than 0.16 (w is half of the width of the liquid-liquid gravity separator), the range of the preferred distance between the baffle and the inlet (lb/w) was from 0.33 to 0.53, and the separation of two phase effect was best when the range of the baffle width (w0/w) was equal or greater than 0.27. After the normalization of the uniformity and turbulence intensity at the baffle plate, the d/w interval should be given priority in analyzing the change rate of the total interval before or after weighting. In addition, there was a good linear correlation between turbulence intensity and uniformity at impingement baffle and baffle plate in the d/w interval, and the turbulence intensity increased with the increase of uniformity.