The invention discloses an amorphous oxide thin film capable of serving as a thin film transistor channel layer and a preparing method of the amorphous oxide thin film. The chemical formula of the amorphous oxide thin film is Zn4In7-xSnxO0.5x+14.5 (0<=x<=7). The preparing method of the amorphous oxide thin film comprises the steps that weighed Zn(NO3)2 6H2O, weighed In(NO3)3 H2O and weighed SnCl2+NH4NO3 are respectively dissolved in dimethylethanol+ acetylacetone+ a 14.5 M ammonia-water solution to from a 0.2 M polymeric pecursor solution respectively, wherein when a Zn source and an In source are prepared, the ratio of the volumes of the dimethylethanol, the acetylacetone and the 14.5 M ammonia-water solution is 25: 1: 0.57 and when an Sn source is prepared, the ratio of the volumes of the dimethylethanol, the acetylacetone and the 14.5 M ammonia-water solution is 25:1:0.285; the mixture is stirred for 6 hours to 24 hours at the temperature ranging from the normal temperature to 50 DEG C, after filtering is conducted, even mixing is conducted according to the fact that the ratio of Zn:In:Sn is 4:(7-x):x (0<=x<=7), and aging is conducted for 4 hours to 24 hours; coating is conducted on a substrate in a spinning mode for film formation and annealing treatment is conducted, wherein the thickness of the thin film ranges from 10 nm to 50 nm. The surface roughness RMS of the prepared thin film is smaller than 2 nm, the carrier concentration ranges from 1014 cm <-3> to 1017 cm <-3>, and the transmittance is larger than 80%; the amorphous oxide thin film serves as the channel layer for preparing a thin film transistor, the threshold voltage ranges from -4 V to 10 V, and the mobility rate ranges from 0.5 cm<2>V<-1>S<-1> to 3 cm<2>V<-1>S<-1>. The amorphous oxide thin film as applied to the thin film transistor has the advantages of being high in mobility rate, capable of reducing the use amount of In, simple in method, low in cost and the like.