Abstract: Jet orifices (e.g.nozzle and perforation) are abundantly applied in petroleum drilling and production engineering.In the case of complex engineering fluid, the flow rate coefficient calculated from jet pressure drop is selected in the large range, so technological design and construction safety are impacted seriously.In this paper, the main factors influencing the calculation of jet orifice pressure drop were analyzed based on the calculation formula of jet orifice pressure drop which is commonly used for drilling, production, fracturing and casing perforation.Then, the formula for calculating the flow rate coefficient of jet orifice at cylinder outlet of taper or arc belt was established by means of numerical simulation.Finally, the identical calculation formula of flow rate coefficient was provided by taking into consideration the effects of physical properties on flow rate coefficient of fluids.And its reliability was verified by virtue of experiments and numerical simulation.It provides the theoretical basis for calculating the pressure drop of jet orifices (e.g.nozzle and perforation) in oil drilling and production engineering.