Abstract: The symmetrical hysteretic nonlinearity system of RCstructures with clearance crack is studied with a piecewise linearsymmetrical hysteretic model. With the equivalent linearizaionapproximate method, the equivalent damping and stiffnesscoefficients are calculated, and the equivalent linearizaion dynamicresponse of symmetrical hysteretic system is obtained. Comparisons aremade between chaotic dynamic characteristics ofchaotic vibro-impact systems with and without clearance crack. The resultsshow that vibro-impact system without clearance crack is in a periodic motion;however, vibro-impact system with clearance crack is often in achaotic motion, and with parameters in a particular range, the system is definitely indisorderly chaotic motion.