Basic princip le of the infrared measuring temperature demarcatingmethod and the BP neural network is introduced. The back Demarcating method of neural network is described in detail. The app lication of Demarcating method neural network in fitting the curves of physical experiments is studied. Through training and simulating under MATLAB, the advantage of usingBP algorithm neural network in physical curve fitting is proven. And its precision is by far higher than the minimum double multip lication fitting so as to offer a new method to dealwith the temperature demarcating software.