The invention discloses a non-excavation in-situ replacement filling spiral drilling method of an unconsolidated stratum. According to the method, an annular space formed at the collapse part of the unconsolidated stratum is utilized to achieve replacement of targeted rock and soil, the most rock and soil are replaced at the most unconsolidated part of the stratum, then a drill bit is tripped in and rotates positively and negatively for pressing and compacting, most clay is extruded in and compacted at the most unconsolidated stratum section, and a formed wall protecting layer is thicker. According to the non-excavation in-situ replacement filling spiral drilling method of the unconsolidated stratum, in the process of pressing, extruding and expanding of the drill bit, a backfill clay layer is extruded tightly and compacted, and meanwhile, an undisturbed soil layer around a drilled hole is extruded tightly and compacted, so that the whole stability of the drilled hole after being processed in this way is improved greatly, and safe, efficient and stable propelling of subsequent processes is ensured effectively. Clayey soil in a put-in hole can use the clay drilled out by other drilled holes or materials are taken at the nearest position. According to the non-excavation in-situ replacement filling spiral drilling method of the unconsolidated stratum, the extra cost is not additionally increased in the process of solving collapse holes, based on the use of original equipment, even clay backfill can also be drilling slag of the other drilled holes, and the cost is saved.