The invention discloses high speed railway cement improved reinforced loess roadbed and a construction method of the high speed railway cement improved reinforced loess roadbed. The roadbed is composed of a reinforced improved cement loess layer, a cement improved loess layer and a compacted loess layer in sequence from top to bottom, and the high speed railway roadbed settlement amount can be controlled at about 5mm by the high speed railway cement improved reinforced loess roadbed and the construction method of the high speed railway cement improved reinforced loess roadbed; by laying a geogrid into the improved cement loess layer and rolling multilayer combination materials, not only is the whole roadbed compression resisting strength and the shearing strength improved, but also the shock resisting property of foundations is strengthened. Compared with traditional high speed railway roadbed processing methods, the settlement is reduced, the vibration collapse of a loess roadbed caused by locomotive vibration can be eliminated, and the physical and mechanical property of loess can be substantially improved; the technology is simple in construction, practical, economical, and capable of guaranteeing high speed train operation safety.