Lanthanum-doped strontium titanate (La_0.3Sr_0.7TiO_3-δ, LST) perovskite is regarded as a promising candidate for high-temperature solid oxide fuel cells (HT-SOFCs) interconnect material due to its good phase stability, good thermal expansion matching to other components, as well as high electrical conductivity in reducing atmosphere. Atmospheric plasma spraying (APS) is a cost-effective processing method to fabricate membranes in SOFCs. However, the LST coatings deposited following the conventional routine exhibit a typical lamellar structure with a limited interlamellar bonding, which dominates the properties of interconnect including gas tightness and electrical conductivity. Besides, the preferential evaporation of Sr during plasma spraying may degrade the performance of LST coatings as interconnect for HT-SOFCs. In this paper, dense LST membranes were deposited on YSZ substrates at preheated conditions by APS. The effect of particle size of LST powders on the chemical composition, phase composition, and electrical conductivity of LST coatings were studied. It was found that the columnar grain growth across lamellar interfaces in LST coatings at the deposition temperature of ~500 °C was highly enhanced with increased interlamellar bonding ratio. Moreover, when the LST particle size is <30 μm, the evaporation of Sr increased remarkably with the decreasing of particle size. When the the LST particle size is ＞30 μm, the evaporation loss of Sr in LST coatings was greatly reduced. A vortex convection model of LST droplets during the spraying process was built to explain the effect of particle size on Sr evaporation. The electrical conductivity and stability of the LST interconnects were tested at controlled atmospheres at an operating temperature of 850 °C. The results show that the electrical conductivity of dense LST coatings prepared with large particles was greatly improved. The LST coatings exhibited excellent phase stability in both reducing and oxidizing atmospheres. Results suggest that LST interconnect with high performance can be deposited by APS through optimizing the microstructure and controlling the chemical composition.