Abstract: An ultrasonic nonlinear approach combined with time reversal technique to visualize the micro-crack in long bones is proposed.The scattered ultrasound generated from the crack in bones contains non-classical nonlinear components.The third harmonic nonlinear component of the probe signals recorded by time reversal array is extracted with a bandpass filter.Then this component is used to focus on the crack through a time reversal process.In the computer simulation,the nonlinear signal contains one or two crack regions were mimicked using the Preisach-Mayergoyz(PM) model,and images of the cracks were constructed.The effect of the crack' radial depth on imaging quality was discussed. This method provides a new technique for noninvasive ultrasonic detection of cracks in bone.