The invention provides a method for ecologically greening coastal saline and alkaline land, which is characterized by comprising the following steps: seeds of syzygium odoratum (Lour.) DC. which has the characteristics of saline and alkaline resistance, water and humidity resistance, fast growth rate, luxuriant foliage, beautiful shape and attractive flowers and fruit are sowed for propagation, after seedlings are 30cm high, the seedlings are transplanted into planting bags with a certain salt matrix and conventionally managed in a seedling nursery, and the syzygium odoratum (Lour.) DC. of two years old is moved out of the seedling nursery to be directly applied to greening the saline and alkaline land and managed by adopting the conventional garden technology, wherein the syzygium odoratum (Lour.) DC. of three years old has the height of over 2m and the crown size of 1m*1m, is green all year round, has red fresh leaves and creates the beautiful landscape. The syzygium odoratum (Lour.) DC. has very good application prospects in coastal saline and alkaline land and coastal beaches in the southern part of China.