The invention relates to a mother-son drill bit spot sampling device comprising a coring pipe, and the coring pipe comprises an inner cylinder and an outer cylinder; the end portion of the coring pipe is provided with a mother drill bit, drill teeth are fixedly installed on the mother drill bit at an interval, a son drill bit is embedded into the mother drill bit, and the mother drill bit is connected with the son drill bit through a locking device; the locking device comprises a locking latch, a baffle plate and a draw bar, the locking latch is arranged in pin holes in the mother drill bit and the son drill bit in a penetrating manner, the baffle plate is connected with the draw bar through a pin, the exterior of the locking latch is sleeved by a latch spring, and the upper end of the draw bar is arranged in the bottom of the son drill bit in a penetrating manner. The mother-son drill bit spot coring device takes fast spot sampling required by coal seam gas extraction effect examination as the technical condition, the mother and son drill bits are locked and drill in a linked manner when sampling is not carried out, an unlocking device is started when a predetermined sampling position is reached, the mother drill bit takes samples in the manner of a sampling pipe, time is saved, positioning is accurate and sample mixing can be avoided, and the aim of fast spot sampling is achieved.