The invention relates to a triangular filtering based suppression method for offset aliasing formed by local slant-stack wave beams. A triangular anti-aliasing filtering operator is completed in the time domain in real time directly, cause-and-effect integration and anti-cause-and-effect integration are carried out on earthquake data, the data can be combined with the time-domain slant-stack wavebeams directly, and the operation of converting the data to the frequency domain for filtering is avoided. At the same time, a weight coefficient is added to an anti-aliasing formula to control the anti-aliasing degree. The anti-aliasing method is completed in the pre-stack data domain, data-domain filtering is carried out according to a slowness component decided by the land surface speed, data after anti-aliasing can be used repeatedly after compression and storage, and the data is not influenced by update of a speed model.