Through the composition design of Q500DZ35 steel plate with the thickness of 265 mm, adopting the clean steel smelting technology, the watercooled ingot casting with independent intellectual property rights, the high temperature, low speed and large reduction rolling technology and reasonable heat treatment technology, steel purity was high, the residual harmful elements were extremely low, and the microstructure of the effective control of the steel plate, refining plate grain, make the comprehensive mechanics performance of steel plate uniform stability, the welding performance qualification test, stable welding performance, the batch production of the Q500DZ35 steel plate with the thickness of 265 mm has been successfully realized, ensuring that all properties of the steel plate meet the technical requirements of the large thickness and high strength steel plate for hydropower station.