Abstract: Mountainous orchards are the majority type of orchards in southern China.This type of orchards usually adapts low plant height and high density cultivation mode, which makes it difficult for mobile spray machines to get into the orchards.Lever operated knapsack sprayers and stretcher mounted sprayer with long flexible pipe are still in use by many orchardists to finish the spray work which makes the task laborious and inefficient.Pipeline spraying technology with no need for moving fulfills the management request of mountainous orchards, and also, it has the characteristics of saving time and vigor.Droplet parameters and droplet spectrum can reflect the droplets size, distribution and uniformity, and meanwhile are the key measures of spray effect.Spray pressure and nozzle pore diameter are the main factors affecting droplet parameters pipeline constant pressure spray facilities.In order to access the influence of spray pressure and nozzle pore diameter on droplet parameters of hollow cone nozzle for pipeline constant pressure spray facilities in orchards, we studied five important aspects of spray performance combined with test platform and laser particle analyzer through measuring droplets scattering spectra of hollow cone nozzle at three types of pore diameter and eight levels of pressure.From such study, we wanted to determine variations of droplet parameters with different pressure and nozzle pore diameter, draw droplet spectrum curves of various working conditions, analyze droplets diameter, distribution and uniformity, and build droplet parameters models based on pressure and nozzle pore diameter.The results showed that the higher the pressure was, and the smaller the pore diameter of the nozzle was, the tinier and the more uniform the droplets would be.Second, at pressure of 0.70-1.40 MPa, data fitting error of three types of nozzles were less than 0.012, which fulfilled the request of experiment.There were not droplets with diameter more than 200 μm.Droplets with diameter 100-200 μm could be ignored because the percentage of them was less than 0.3%.The diameters of the majority droplets(> 99.728%) were less than 100 μm.The percentage of droplets with diameter less than 50 μm was 86.786%-98.706%, and the percentage of droplets with diameter less than 40 μm was 79.659%-93.374%.There were mainly droplets with diameters 20-50 μm in droplet spectrum curves, and droplet spectrum peak appeared at 30 μm.Volume median diameter(VMD) of droplets was 30.610-32.317 μm, and diffusion ratio(DR) was 0.893-0.916.Droplets were all tiny and uniform, and the majority type was aerosol.Third, at pressure of 0.70-1.40 MPa, VMD of droplets was 30.610-31.632 μm, and DR was 0.901-0.916.Droplets were tinier and more uniform, and the type was aerosol.When the pressure was more than 0.80 MPa, spray effect were better.The relationships between VMD and DR of droplets, and pressure could both be described by quadratic polynomial equations (R2>0.968), and meanwhile, VMD and DR of droplets influenced by pressure and pore diameter could both meet the binary linear equations(R2=0.928, 0.937).The results have verified the importance of studying pipeline constant pressure spray system, and meanwhile provided basis for selecting nozzle, optimizing pipeline constant pressure spray system, setting spray pressure and optimizing spray effect.