The paper relates to the field of hydraulics and is devoted to the study of fluid flow states in a non-submerged Venturi channel. The aim is improvement of the method of hydraulic calculation of the classical Venturi channel. Authors applied experimental methods with the use of hi-tech certified measurement equipment allowing for digital technology-based automated collection and processing of empirical information; calculation and analytical methods. Distribution of depths, velocities and Froude numbers in flow direction inside the classical Venturi channel water gauge are obtained. The theoretical method of hydraulic calculation of the full-capacity discharge of the Venturi channel is considered, which does not contain empirical coefficients. It is established that the calculation of the full-capacity discharge of the classical Venturi channel in accordance with the current State Standard of the Russian Federation MI 2406-97 gives underestimated values of the design flow rate with the actual flow rate with a systematic error of more than -2 %, the theoretical method of hydraulic calculation of the full-capacity discharge of the Venturi channel has a relative error of ±1 %.