A simple unified fuel spray model is proposed. The model covers the main physical processes of the fuel spray: jet spray penetration, fuel atomization and evaporation, air entrainment and mixing. The model is aimed at dealing with a wide range of the jet spray regimes: free jet, normal and oblique jet-wall impingement, wall jet and swirling jet.A new formula of the jet spray penetration is suggested based on the jet entrainment law and momentum conservation. For different jet regimes the entrainment coefficients are determined from the basic turbulence relation of the jet flow. A dynamic model of the jet spray atomization is described based on the energy conservation. The jet atomization model can evaluate the variation of jet droplet Sauter diameter with time. For the oblique jet-wall impingement an approximate solution of angular distribution of momentum for outflow jet sheet is given in a cubic polynomial form based on the mass and momentum conservation of inviscid jet flow.For the various jet regimes the model is validated with a range of published jet spray data. The prediction accuracy is satisfactory. The model applications are also described to analyze the effects of injection parameters, impinging and swirling flows on air-fuel mixing processes of the jet spray. These results show that the present model is a simple but informative approach to simulate the jet spray mixing process.