The mixture formation processes of diesel spray were quantitatively analyzed in this paper.The LAS(Laser Ab-sorption-Scattering)technique was applied to investigate the vapor/liquid phase concentration distributions in diesel spray which was formed in a high-pressure and high-temperature constant volume vessel.To satisfy the requirements for LAS test fuel(the fuel should absorb ultra violet light but not absorb visible light,and the image should be clear but without saturation),the Tracer LAS technique was newly developed.A tracer fuel with 97.5 volume per-cent of n-tridecane and 2.5 volume percent 1-methylnaphthalene(a-MN)was employed.The ntridecane plays a role as the basis diesel fuel to simulate the diesel fuel spray evolution behaviors and the a-MN plays the part of UV beam tracer to quantitatively analyze the concentration distributions.From the comparison of mass of fuel vapor at completely vaporized by the LAS technique and injection amount,its measurement accuracy can be discussed.The piezo-actuated single hole nozzle injector with a diameter 0.133mm was employed.In this research work,the diesel spray structure,and the vapor/liquid phase concentration distributions were concentrated on and the effects of injection amount and injection pressure on diesel spray formation were discussed.