The invention discloses an ecological greening method for a side-slope of a highway, which comprises the following steps: 1), after a slope surface is leveled, soil dressing is backfilled, a trench is excavated and a drainage facility is built, net laying and fixing are conducted, and pre-prepared farmland surface soil and base fertilizer are covered on a three-dimensional net by adopting a three-dimensional vegetative net slope protection technology; 2), seeds of salvia farinacea and vervain are soaked in warm water till being swelled; 3), the swelled seeds are sowed on a seedbed, covered with the farmland surface soil, pressed lightly, and subjected to water spraying and maintenance; 4), when seedlings germinated from the seeds are 6-8cm, seedling thinning is conducted; and 5), an ecological green belt of the side-slope of the highway is formed after 2 years of growth of the seedlings. According to the method, the growth rates of the salvia farinacea and the vervain are relatively high; the greening success rate is high; a greening ecological effect and a landscape effect can be achieved quickly without special maintenance; and the purposes of preventing light and dazzle, guiding sight of a driver, improving a landscape and the like can be effectively achieved. Therefore, the method can be widely applied to the greening of the side-slope of the highway, and is very good in application prospect.