The invention relates to a dry-process well cementation low-density cement paste for oil-gas well cementation and a preparation method of the dry-process well cementation low-density cement paste. Thedry-process well cementation low-density cement paste for oil-gas well cementation contains the following components in parts by weight: 100 parts of cement, 1-60 parts of lightening admixture, 1-40parts of fluid loss agent, 0.1-20 parts of set retarder, 1-50 parts of filler, 0.1-10 parts of defoaming agent, 0.1-10 parts of fibers, 0.1-10 parts of fruit husks and 20-150 parts of water. The dry-process well cementation low-density cement paste for oil-gas well cementation, disclosed by the invention, has good flowability, low in water loss and good in water losing and wall building effects and has relatively strong plugging capacity when suffering from cracks. The dry-process well cementation cement paste can be directly adopted for well cementation after air drilling, so that the transformation period of the paste can be greatly shortened, the drilling period can be shortened, the drilling cost can be reduced, and the development of an oil-gas field can be accelerated.