A mini fixed focus lens module is provided. From an object end to an image end thereof, the mini fixed focus lens module sequentially includes a first lens, a second lens, a third lens and a fourth lens. The first lens has a positive diopter, the second lens has a negative diopter, the third lens has a positive diopter, the fourth lens has a negative diopter, a combined diopter of the second and third lenses is positive, and the mini fixed focus lens module satisfies the following formula: 0.2