This paper designs a novel impedance transformer used for low frequency, performing 150 Ω at the input to 50 Ω at the output within the range of 0.1 GHz to 3 GHz. The novel impedance transformer is characterized by bandnotch function through loading the technology of curving split rectangular loop with good resonance. The principle is based on the impedance transmission characteristics of Balun impedance transformer and the resonance characteristics of split rectangular loop. The results indicate that the S12 parameters are below minus 15 dBi and the S11 parameters are above minus 0.5 dBi.And the bandnotch frequency point can be controlled by changing the length and location of the split rectangular loop. The HFSS software is utilized for modeling and optimizing parameters. The results of S parameters and fabricated sample measurements indicate that the design is reasonable. Taking bandnotch impedance transformer as the antennas matching terminal, there is a good prospect in application in the fields of radiation frequency harvest and the matching of extremely wideband antenna arrays.