The invention discloses a simple method for pore-forming and pile-forming after a cavity encountering of a rotary drilling rig. The simple method comprises the steps that 1, a pile position is determined; 2, protective piles are correspondingly constructed outside the two ends of acavity in the construction area to block the two ends of the cavity; 3, pile holes separated from the protective pilesin the pile position are excavated, the protective pile holes at the end head are directly filled with excavated good soil, and compaction is conducted by filling the soil; 4, a method of hole separation construction is adopted, the pile holes of each pile in the construction area are firstly excavated to the cavity, the pile holes are filled with the good soil of the adjacent pile holes and compacted until full compaction is achieved; 5, the pile holes skip-excavated in the middle is excavated again, soil filling and compaction are conducted until the construction of all the pile holes is completed; and 6, from the middle of the construction area, a conventional technology is adopted to complete the pile-forming construction in all the construction areas. The simple method has the advantages that under the condition of almost no increase in cost and no increase in construction period, all the pile construction at the cavity is completed, and the economic, environmental-friendly and social benefits are significant.