Abstract: To study the possibility of detecting the crossing channel by using a traditional logging tool, acoustic field generated by a monopole source in a cased well with a crossing channel of various angles is simulated by 2.5-D finite difference method for the first time. Snapshots of normal stress and synthetic time-domain waveforms are displayed. The two-dimensional spectrum in wave-number and frequency domains is also calculated, where the influence of the channel is clearer than that in the waveforms. Numerical study demonstrated that a crossing channel can be detected and sized if its angle is greater than 30 degree, and larger offset and lower frequency source are favorable to detect and size the crossing channel.