A bi-function headlight assembly comprising a multi-focal collimating lens, at least a first light source, and a second light source, wherein the first light source is a low beam light source and the second light source is a high beam light source, and wherein a bi-function is defined by lighting one or more of the first light source and the second light source; the multi-focal collimating lens comprising, with the relative positions referring to the mounting position of the multi-focal collimating lens within the bi-function headlight assembly: a lower collimating lens part comprising a lower collimating lens portion and two total internal reflection lens portions arranged on a left side and a right side of the lower collimating lens portion; an upper collimating lens part located on top of the lower collimating lens part and comprising an upper collimating lens portion and two total internal reflection lens portions arranged on a left side and a right side of the upper collimating lens portion; one focal point of the lower collimating lens part being located on a vertical symmetry plane of the lower collimating lens part, and two focal points (105, 105') of the upper collimating lens part being symmetrically located on both sides of a vertical symmetry plane of the upper collimating lens part; a lower edge of a light emitting area of the first light source being located on a line connecting the two focal points (105, 105') of the upper collimating lens part, and the focal point of the lower collimating lens part being located on a light emitting area of the second light source; an upper edge and lower edge of the multi-focal collimating lens being shaped based on the focal point of the lower collimating lens part and the two focal points (105, 105') of the upper collimating lens part such that images formed by the light sources (106, 107) constitute a far-field light pattern with a clear cut-offline. a lower collimating lens part comprising a lower collimating lens portion and two total internal reflection lens portions arranged on a left side and a right side of the lower collimating lens portion; an upper collimating lens part located on top of the lower collimating lens part and comprising an upper collimating lens portion and two total internal reflection lens portions arranged on a left side and a right side of the upper collimating lens portion; one focal point of the lower collimating lens part being located on a vertical symmetry plane of the lower collimating lens part, and two focal points (105, 105') of the upper collimating lens part being symmetrically located on both sides of a vertical symmetry plane of the upper collimating lens part; a lower edge of a light emitting area of the first light source being located on a line connecting the two focal points (105, 105') of the upper collimating lens part, and the focal point of the lower collimating lens part being located on a light emitting area of the second light source; an upper edge and lower edge of the multi-focal collimating lens being shaped based on the focal point of the lower collimating lens part and the two focal points (105, 105') of the upper collimating lens part such that images formed by the light sources (106, 107) constitute a far-field light pattern with a clear cut-offline.