Based on the mixing method theory， in order to study the nonlinear ultrasonic non-collinear mixing method， and to verify the feasibility of the two columns of incident fundamental waves scattering out the mixing wave， a test system was set up with discussing the most suitable excitation amplitude. On this basis， the non-collinear mixing method was carried out at the mortar test blocks with lengths and angles of prefabricated cracks. The relationship between the crack length， angle and the ultrasonic nonlinear coefficient was analyzed. As a result， 100 V is the best excitation amplitude in non-collinear mixing detection. The nonlinear coefficient of the mixing frequency gradually increases as the length and angle of the crack increasing. The amplitude of the mixing frequency has a similar trend. To verify the reliability of the non-collinear mixing method， the comparison with the test results of the higher harmonic ratios method shows that the nonlinear coefficient of the former is more sensitive to the change of the length and angle of the crack than the other one. Those proves that the non-collinear mixing method can be used for the damage detection of heterogeneous materials such as concrete.