The aim of this work was the estimation of P pressure during InP synthesis process, by HGF (Horizontal Gradient Freeze) method in quartz reactor. It was done in high pressure, multizone computer control furnace. Design of the furnace and P pressure control in quartz reactor by temperatur profile control in furnace are described. Results of temperature measurements in phosphorus zone of reactor and their influence on evaporation dynamics are desired to obtain safety process of InP synthesis.