Abstract: Based on the dynamic impedance of a massless rigid disc buried in a coupled seawater-seabed half-space (He and Wang, 2013), the horizontal vibration of a widely used deeply buried plate anchor is studied, which is subjected to a constant vertical pull force and with self-weight, under harmonic horizontal wave loads. Simplified formulas to calculate the resonance frequency and magnification factor are given. By using parameters of a real seabed and plate anchors, it is found that the resonance of the deeply buried plate anchor can be avoided if the thickness to radius ratio of the anchor satisfies some requests. For real plate anchors, it is very easy to satisfy the requests. Besides, the horizontal displacement of the deeply buried plate anchor seems to be independent of the frequencies of the wave loads, and the largest horizontal displacement occurs when the wave load frequency is 0. The results of this study will be helpful for understanding the horizontal vibration characters of the widely used deep sea plate anchors.