The invention discloses a medium-temperature aluminum-based foil strap brazing material and a preparation method thereof. The brazing material comprises the following components by mass percentage: 6.5-9.6 of Si, 16.0-20.0 of Cu, 8.0-10.0 of Ge, 2.0-6.0 of Zn, 0.5-1.0 of La and the balance of Al. The brazing material is prepared by rapid cooling of a melt, the melting point is lower than 495 DEG C, a foil strap is suitable for brazing of aluminum alloy with the solidus temperature higher than 520 DEG C, torch brazing, induction brazing, furnace brazing, gas protection brazing and the like can be performed, the brazing temperature is 510-520 DEG C, and the brazing material can be applied in brazing of precision components made of aluminum alloy. When the brazing material is used with 5083 aluminum alloy for QJ201 brazing, the shear strength of a brazed joint is higher than 80MPa.