The smaller radial dimension and its influence on the loss in energy are considered, when the hydrocyclone is applied to downhole. To study the pressure characteristics of hydrocyclone applied to the injection-production system for the same well, the indoor test process flow is built up. Tests have shown that the pressure loss is increasing and the small cone section is still the main separated section with the accrescent flow and split ratio. The split ratio is lower as small as possible on condition that the technological requirements are fulfilled. In comparison with the inlets with different channel types, when the radial dimension is decreased, the hydrocyclone, which has the inlet of beeline channel type with changing sections, can allocate the energy more reasonably and decrease the unnecessary pressure loss.