The invention provides a buoy-based long-time on-line monitoring apparatus for the sea cloud height. The apparatus comprises a buoy; and a laser ceilometer, a buoy attitude measuring module, a cloud height correction and compensation module, a communication module, and a meteorology and hydrology observation sub system. The buoy attitude measuring module is used for measuring attitude parameters, like a heading parameter, a rolling parameter and a pitching parameter, of a buoy platform; the cloud height correction and compensation module is used for realizing cloud height observation correction and compensation based on the attitude parameters of the ceilometer; and the communication module is used for uploading the data that can be used by users. According to the invention, buoy-based laser radar cloud height observation is carried out and the measurement result is accurate and reliable; off-shore, long-term continuous, real-time, high-precision, high-temporal-spatial-resolution marine environment monitoring on the cloud height, cloud thickness, and conventional marine meteorology and hydrology can be realized; an accurate and reliable data support can be provided for scientific researches of marine atmosphere, weather forecasting, ocean shipping, and naval drills and the like; and thus the apparatus has important significance in development of multiple fields like the marine economy, the marine science and technology, and the legal rights safeguarding on the sea.