Determining method and system for second interface cementing quality of cement sheath

The invention provides a determining method and system for second interface cementing quality of a cement sheath. The method comprises the steps that six full waveforms which are received in a short spacing mode and used for measuring the upper portion or the lower portion of a sonic system are selected from 24 waveforms recorded by a cement cementing imaging and logging instrument, wherein a well cementation inner wall is covered with the six selected full waveforms along the propagation path from a transmitter to a receiver by at least one turn, and sub-waves are extracted from the six selected full waveforms respectively; according to the extracted sub-waves, reflected waveforms, from the outer side of the cement sheath, in the six full waveforms are extracted respectively based on the least square deconvolution algorithm, wherein each reflected waveform corresponds to one sector of well cementation; the waveform energy of all the reflected waveforms is calculated, and the cementing quality of the second interface of the cement sheath in the sector corresponding to the corresponding reflected waveform is judged according to the waveform energy. According to the determining method and system, semi-quantitative estimation can be performed on the cementing quality of the second interface.