In recent years， with rolling out of marine natural gas hydrate exploration， in order to further increase the production and accelerate the pace of commercial exploitation of marine natural gas hydrate， the development of horizontal wells has become an important means for increasing production. However， in horizontal well drilling in shallow soft formation where shallow soft digenetic formation is present， the key technologies for borehole cleaning， wellbore stability， rheological property control， lubrication， friction reduction and leakage prevention in highly deviated well sections and horizontal well sections should be solved. In view of the technical difficulties on drilling fluid for horizontal wells in shallow soft formation， indoor research and field test were conducted to form a set of drilling fluid system and drilling fluid drilling process for horizontal well drilling in shallow soft formation， and several horizontal test wells were drilled in shallow soft formation on land to ensure the smooth well drilling and completion， which provides a large number of field test data for trial production of marine gas hydrate horizontal wells in China.