The engineering investigation was researched for offshore wind farm. On several occasions the soil conditions had proven to be a key area for offshore wind farm. The offshore engineering investigations, usually based on survey, test, simulation and analysis methods, were established information about seabed topography, seafloor soil, and offshore environment. The principle and procedures of engineering investigation were studied, offshore site conditions were analyzed for meteorological conditions, oceanographic conditions, soil conditions, seismic activity, biology, and various human activities, and engineering investigations were researched to various foundation types, and time schedule for offshore engineering investigations was established. Experience of engineering investigations was put forward to combine with foreign offshore wind farm. The engineering investigations provide project basis of various structure on offshore wind farm.