In order to study the influence of the preferential flow formed in the facture by light non-aqueous phase liquids (LNAPLs) in the unsaturated zone on contamination of the aquifer, we experimentally investigated the migration behavior of the preferential flow formed in a single fracture by LNAPLs with different viscosities in the unsaturated porous media, selecting soybean oil and No. 0 diesel fuel as two LNAPLs with different viscosities. The results indicate that the LNAPL with lower viscosity forms a faster preferential flow in the fracture, and, after entering the capillary zone, the LNAPL migrates more slowly in the vertical direction, and disperses faster in the horizontal direction under the action of uplift force. The preferential flow not only occurs in fractured heterogeneous media, but also exists in homogeneous media in the form of finger flow, and the LNAPL with larger viscosity tends to form more narrow finger flows.