According to drilling encountered boulder in deep sand gravel stratum in Yarlung Zangbo River Leng-da hydropower station, a scalable two-wing reaming bit was used to solve pipe blocking. By enlarging a hole in the boulder under the casing, the hole diameter is slightly larger than the outer diameter of the casing pipe to ensure the casing going down to the planned depth. This method can not only avoid the danger and complexity of hole blasting shattering boulder but also can overcome casing wear, broken and high cost caused by high torque of casing bit drilling for casing following. This process is easy to master with no limitation of hole depth and can be popularized in pipe-following ream drilling, even in hole accidents treatment.