A simple model describes the dynamic parameters of gas and particles in a cylindrical heavily laden jet. Analysis showed that the gas-particle jet flowing out of the nozzle might be considered as isobaric if parameters of the jet at a nozzle cross-section are uniform. Radial gas velocity is linearly distributed along the jet radius. The model of the jet is quasi-one-dimensional in this case. Assuming the jet to be incompressible an analytical solution of the momentum equation was derived. The results obtained with the model were compared with numerical results obtained by solving the axisymmetric problem using the "Fluent" numerical code. The model provides acceptable estimations for initial jet sections (length is less than double nozzle diameter) if solids/gas flow ratios lower than 6-8 and can be used for rough estimations at high solids/gas flow ratios (up to 50). This model is feasible for particle sizes within the range of 20 less than or equal to d(s) less than or equal to 200 mum.