Abstract: When bored pile construction is carried out in some complex terrain environments, various problems are very easy to occur, thus aff ecting the construction safety and engineering quality. For example, when drilling in karst development zone. The conventional operation method is to use impact drill to throw and fi ll or steel casing to follow up after punching. The traditional operation method is easy to cause dangerous situations such as collapse and slurry leakage in karst terrain. In order to better improve the drilling quality under complex construction conditions, this paper takes the complex karst terrain environment as the concrete analysis object,and analyzes the concrete construction scheme of pile foundation casing full-return drilling machine, in order to promote the effi ciency and quality of construction operation under complex environment.