The invention discloses an ultrasonic guided-wave defect locating method based on Liapunov index, and the method is as follows: constructing a duffing oscillator signal detection system on the basis of duffing equation, calculating the Liapunov index variable with driving force F change; exciting ultrasonic guided wave signals on a to-be-tested material through an emitter, traversing all positions of the to-be-tested material with the ultrasonic guided wave signals, and obtaining an actually measured signal by a receiver; constructing a window function, intercepting, from the actually measured signal, interception signals with length corresponding to different window length, inputting each interception signal into theinterception signal, calculating the Liapunov index with driving force F change after the interception signals are inputted; determining the interception signal corresponding to the window length of greatest driving force F change amount, moving the window function to scan the interception signal for defect locating of the to-be-tested material. The ultrasonic guided-wave defect locating method can be used for ultrasonic guided wave signal identification, locating of defects in different degrees of injury, and improvement of the sensitivity of ultrasonic guided wave identification of small defects.