Abstract: In order to find an exact description of jet formation process for the high pressure liquid injection,it is difficult to photograph the mechanism of the liquid jet breakup in the vicinity of the nozzle,because the jet core is hidden behind a curtain of spray cloud.The system built by authors uses flash X-rays to study the liquid jet breakup processes.Radiography can hardly resolve the spray cloud,but it is capable of recording the full jet structure and allows to determine the intact core.As examples some liquid jet radiographs have been taken at different fluid pressures and nozzles.The point of cylindrical jet disintegration and the point of annular jet coalescence shift to the nozzle orifice with increasing prepressure.