Based on Fluent software, using standard model and with other parameters selecting emporical values, makes numerical simulations of the flow field of different area ratios in annular jet-pumps. Calculates the performance parameters of the jet-pump of two type injecting angles and analyses the effect of different area ratios on the efficiency. The results indicate that the highest efficiency is at the area ratio of 1/3. According to the principle of the highest efficiency reducing 3％, the optimal area ratio is between 0.3 to 0.35.