The Pliocene Yinggehai Member 2 of Dongfang Gasfield in Yinggehai Basin is characterized by littoral and shallow marine facies, which is mainly composed of thick mudstone intercalated with low permeability siltstone. In order to realize the sustainable development and utilization of natural gas in Dongfang Gasfield, it is urgent to clarify the "sweet spot" distribution of low permeability reservoir. Taking the Ⅰgas formation of Yinggehai Member 2 (N2y2-Ⅰ) of Dongfang Gasfield as an example, based on the comprehensive application of 3D seismic data, logging data, production data, and other data, the research on prediction and classification of "sweet spot" in low permeability reservoirs is carried out by the use of logging constrained sparse pulse inversion method, and the analysis of the main controlling factors (sedimentary microfacies) of "sweet spot". The results show that the P-wave impedance of the low-permeability gas-bearing reservoir ("sweet spot") in N2y2-Ⅰ is less than 5.6×106 (kg/m3·m/s). The classification and identification criteria for "sweet spot" of low permeability reservoirs has been established through the crossplot analysis of P-impedance between porosity, permeability, water saturation, and thickness in N2y2-Ⅰ. There are three types of "sweet spot". The type Ⅰ is located in the main body of shoreface bar, with the P-impedance less than 5.0×106 (kg/m3·m/s), the permeability more than 20×10-3 μm2, the production more than 10×104 m3/(d·m), the thickness of gas formation more than 10 m, and the water saturation less than 55，. The typeⅡ is also located in the main body of shoreface bar, with the P-impedance among (5.0-5.3) ×106 (kg/m3·m/s), the permeability among (10-20)×10-3μm2, the production among (5-10) ×104 m3/(d·m), the thickness of gas layer among 5-10 m, and the water saturation among 55，-65，. The type Ⅲ is located at the edge of shoreface bar, with the P-impedance among (5.3-5.6) ×106 (kg/m3·m/s), the permeability less than 10×10-3μm2, the production less than 5×104 m3/(d·m), the thickness of gas formation less than 5 m, and the water saturation more than 65，. Generally, the "sweet spot" of type Ⅰ and type Ⅱ are mainly distributed in strips in the main body of shoreface bar, the type Ⅲ is distributed in flaky shape on the edge of shoreface bar. This method is mainly applicable to the reservoirs with obvious P-impedance difference, and its reasonable application can effectively determine the plane distribution of "sweet spot", so as to provide guidance for the sustainable development of oil and gas fields.