The invention discloses a pre-consolidation construction method for a completely weathered stratum. The pre-consolidation construction method is characterized in that cement grout materials are filled in gaps among particles of the completely weathered stratum, an intensely weathered stratum or a covering layer under certain pressure, and after solidification of the cement grout materials, consolidated bodies are formed by mixing the particles with grout. The pre-consolidation construction method particularly includes steps of trimming slopes so that the ratio of the slopes ranges from 1:1 to 1:1.3; measuring and setting out hole positions; performing drilling with casing in a non-irrigation section and embedding orifice pipes in the non-irrigation section; forming a hole in a first section by means of drilling with casing; mounting a grouting shock pipe; pulling up the orifice pipe; grouting; waiting for solidification of the cement grout materials, and cleaning the drilled hole; and performing acceptance check. The pre-consolidation construction method is high in pertinence and reliable in technology, construction procedures are simple, operation is simple and convenient, cost is low, and steel materials are saved as compared with other supporting measures such as steel tubular piles. Besides, as compared with the other supporting measures, a ground for implementing the pre-consolidation construction method is easy to arrange, project progress is fast, and the pre-consolidation construction method is favorable for providing operation conditions for follow-up working procedures in time.