The invention provides a premixed flow-state solidified soil foundation trench backfill construction method. The method comprises the steps of solidified soil preparation, foundation trench cleaning,gravel drainage ditch construction, formwork erecting, layered pouring, surface scraping treatment, field finished product protection, solidified soil maintenance and the like. The method is convenient and fast in construction process, economical, convenient in material obtaining, good in stability, high in compactness, good in self-sealing performance and impermeability, and short in constructionperiod, compared with a traditional backfill construction mode that a small excavator and a tamping machine are used for backfilling, chute backfilling is used, vibration is not needed, layered construction joint faces can be well combined without chiseling, construction joints cannot be formed, and the problems that in traditional backfill construction, the construction difficulty is large, thebackfill construction period is long, and the backfill quality is difficult to control are solved.