Embodiments of the invention provide a method for calculating material impedance inside and outside casing pipe, a method for determining a relationship between material impedance inside and outside casing pipe and Lamb wave attenuation, a method for determining a relationship between material impedance inside and outside casing pipe and resonance wave resonance efficiency, a method for evaluatingwell cementation quality, and a computer device. The method for calculating the material impedance inside and outside casing pipe includes: setting a Lamb wave measurement device and a resonance wavemeasurement device to point to a same position inside the casing pipe, to obtain a Lamb wave attenuation measurement value and a resonance wave resonance efficiency measurement value; and obtaining avalue of the material impedance inside and outside the casing pipe through calculation according to the Lamb wave attenuation measurement value and a predetermined first function relationship betweenthe material impedance inside and outside the casing pipe and the Lamb wave attenuation, and according to the resonance wave resonance efficiency measurement value and a predetermined second functionrelationship between the material impedance inside and outside the casing pipe and the resonance efficiency. The solution in the embodiments of the invention improves accuracy of inversion of the material impedance after the casing pipe, and can simultaneously calculate acoustic impedance of a fluid material in the casing pipe.