Abstract: This research shows results of calculation of friction resistance of end plates affecting tendencies of free flat jet behavior. Flow diagram of jet flowing among end surfaces is built up. Estimate of friction at turbulent boundary layer is fulfilled. Calculation formula for the first study which describes variation of maximum jet velocity at a first approximation is acquired. These calculation data are compared with the experimental data. Also, a theoretical calculation of the second study was conducted. For this study calculation formula about the maximum velocity variation was received.