For traditional combustion chambers, when the working condition deviates from the design point, the combustion efficiency will be greatly reduced, and harmful products such as NOx, CO and UHC will increase greatly. This brings huge waste of fuel and air pollution. In order to improve the combustion efficiency at off-design conditions, in this paper a new method using a circular transverse jet as a means of fuel injection, fuel/air mixing and flame stabilization is explored, and an innovative configuration of transverse jet device is developed. Accordingly, the circular transverse jet is studied numerically and experimentally. It is found that the unique aerodynamic structure and high turbulence intensity of the circular transverse jet give an efficient mixing of the fuel and the mainstream along the fuel jet trajectory. Although the deviation of the total excess air coefficient is far from 1, a uniform mixture is formed in the recirculation zone downstream of the jet with an excess air coefficient approaching to 1. Experimental results show that the average excess air coefficient in the recirculation zone is about 1.29, and the combustion efficiency reaches more than 99% at the end of the recirculation zone when the overall excess air coefficient is 10.5, even under the low pressure and temperature conditions. These results demonstrate an effective improvement of the combustion efficiency at off-design conditions by the method proposed in this paper. In addition, the flow field structure under the interaction of circular transverse jet with mainstream, the distribution characteristics of gas components and temperature in the combustion zone are studied, which laid the foundation for the further study and the engineering application of this method.