我国的“三线”建设三线的划分范围新中国成立后，为了适应当时战争的要求，按照设想的军事地理区域，将中国沿海划分为第一线，中部为第二线，后方为三线，又分为大三线和小三线，大三线包括西南的四川、云南、贵州和西北的甘肃、陕西、宁夏、青海等；小三线是指中部及沿... After the founding of New China, in order to meet the requirements of the current war, China’s coastal areas were divided into the first line, the second line to the middle and the third line to the third line according to the envisaged military and geographical region. Big Three and Small Three, Big Three including Southwest Sichuan, Yunnan, Guizhou and northwestern Gansu, Shaanxi, Ningxia, Qinghai, etc .;