In principle, compressed air injection into a convergent-divergent nozzle is a well-known technique to improve a waterjet propulsion system’s thrust force. However, instead of using compressed air, atmospheric air with the pressure difference between the throat and the divergent section can be feasible. This paper attempts to determine the impact of atmospheric air injection on the outlet mixture velocity within a novel convergentdivergent nozzle, which improves thrust force. Air mass flow rate and inlet water velocity on the average outletmixture velocity and thrust force are investigated. Two different geometrical configurations (i.e., Configuration I (with an obstacle) and Configuration II (without obstacle)) of the nozzle are studied in depth. A three-dimensionalnozzle is modelled with air injection in the water flow. Two-phase modelling has been employed, and the solution was obtained using ANSYS-Fluent^®. The results suggest an improvement in outlet velocity with an increase in air mass flow rate and inlet water velocity. Also, the presence of obstacle hinders the proper mixing between air and water. These findings reveal that for an air mass flow rate of 0.003 kg/s and inlet water velocity of 3.7 m/s, there is a 60 % increment in the thrust force for Configuration II than Configuration I. Therefore, the resultant findings show that the proposed novel convergent-divergent nozzle is a feasible alternative against compressed air injection, reducing the overall load and cost involved.