In the ultra-deep and ultra-shallow reservoirs （“double ultra” for short）， problems exist such as difficult coring operation， low success rate， high operation cost， and lack of reference experience. In view of this， the analysis of the coring difficulties without risers is carried out， the corresponding technical countermeasures are put forward， and a set of efficient coring scheme is formed. The results show that in the “double ultra” environment， the reservoir is dominated by unconsolidated and loose argillous sandstone， and the coring operation faces the problems and challenges of “blocked core”， the difficulty of controlling displacement and bit weight， and the high cost of ultra-deep water operation. The Rb-8100 fully enclosed conserved coring tool and HSC043-8100 coring bit are selected， corporated with small perameter mode of small displacement （200L/min）， low speed （15~40r/min） and stepped bit weight （2~10t）. The self-made net diverts seawater at the bit and protects the bottom core. The pilot test of riserless coring was carried out in “double ultra” gas field in South China Sea， and the core recovery reached 100%. It is the first time to realize the efficient coring operation in “double ultra” reservoirs， and lays an important foundation for the later development of ultra-deep and ultra-shallow reservoirs gas field.