The mixing of magnetic and electronic CTs in transmission line might affect the correction of line differential protection′s action. Recently, the virtual braking current method is the common way to solve that problem. While the virtual braking current method is fixed to the threshold value of the differential protection, and the influence of the variation of the line parameters is not considered, therefore the opening time of differential protection takes too long. Aiming to this, it proposes an improved method to identify saturation in this paper, which is based on floating threshold value. Firstly, it calculates the line parameters and floating threshold value of the reference curve by the establishment of the model of current transformer which obtains line parameter and relationship of saturation degree. Secondly, the threshold value is chosen adaptively according to the specific line parameters to ensure the differential protection disoperation, as well as reducing the locking time of differential protection. The simulation results show that the method can enhance the sensitivity, reduce the shutting time of differential protection and can apply to a large scale.