A numerical investigation is performed to study the flow fields inside the specific mixer-ejector, composed of a lobed nozzle and a curved mixing duct with a large-aspect-ratio outlet. The effects of guide baffle number (n) and outflow angle (β) on the pumping performance are illustrated. When compared to the conventional no-baffle situation, the presence of guide baffles is demonstrated to improve the flow uniformity of mixing flow in the vicinity of exhaust outlet and reduce the static pressure of secondary flow passage at the primary nozzle exit. With the increase of guide baffle number the pumping coefficient is raised monotonically. However, beyond n=8, the guide baffle number has nearly no influence on the pumping coefficient. With respect to the conventional no-baffle situation, the pumping coefficient could be increased about 20% by the presence of outflow guide baffles at the best. With the increase of guide baffle outflow angle, the pumping coefficient takes on a first-increase and then-decrease tendency. An optimum outflow angle appears at β=78° approximately, achieving the maximum pumping coefficient and better total pressure recovery coefficient.