High fuel injection pressure has been regarded as a key controlling factor for internal combustion engines to achieve good combustion performance with reduced emissions and improved fuel efficiency. For common-rail injection system (CRS) used in advanced diesel engines, fuel injection pressure can often be raised to beyond 200 MPa. Although characteristics of diesel spray has been thoroughly studied, little work has been done at ultra-high injection pressures. In this work, the characteristics of CRS diesel spray under ultra-high injection pressure up to 250 MPa was investigated. The experiments were conducted in an optically accessible high-pressure and high-temperature constant volume chamber. The injection pressure varied from 50 MPa to up to 250 MPa. Both non-evaporating condition and evaporating condition were studied. A single-hole injector was specially designed for this investigation. High-speed Mie-scattering imaging was used to capture the global structure of the liquid sprays. In addition, high-speed microscopic back-lit imaging was used to obtain detailed information of sprays near the nozzle. Results show that, increase of injection pressure improved the injection responsibility and spray atomization. A correlation of injection rate and the velocity of initial spray was observed by time-resolved imaging.