NaLuF4 doped Yb/Tm upconversion phosphor was synthesized by a facile hydrothermal method, using EDTA as a chelating agent. The influence of synthesis parameters was investigated on UV emission intensity through face-centered central composite design (CCD). Four parameters including F:RE ratio, pH value, reaction time and ethanol percent were considered as independent variables. It was found that pH value and F:RE ratio have the highest effect on emission intensity and the ethanol percent and the reaction time have mild and low influence on it. Furthermore, at pH 4, nano spherical particles with cubic phase were formed and change of other parameters had low influence on phase transformation. However, the hexagonal micro prisms with the hexagonal phase were predominant at pH ≥ 6. The role of EDTA was indicated on phase transformation and aggregation of particles at the various value of pH. It was shown that the crystal phase, the surface smoothness and the particle size are influential factors on UV emission intensity.