Abstract: As an important part of the power module in offshore wind power converter valves, the high voltage direct current (HVDC) capacitors are the core component with the lowest degree of localization in converter valves. The dielectric and energy storage characteristics of biaxially-oriented polypropylene (BOPP) films directly affect the voltage level and capacity of capacitors, which are largely dependent on imports at present. With the development trend of capacitor compactness as well as the challenge of long-term safe and stable operation under complex operating conditions, we researched the key parameters of selection for polypropylene (PP) materials. Based on the investigation and selection of existing PP materials from major capacitor manufacturers at home and abroad, combined with experiments and analysis of micro structures, crystallization parameters and electrical properties of granular and film samples, it is found that the key factors affecting the dielectric and energy storage characteristics of PP materials include isometric, ash, crystallization parameters, loss and leakage current under high temperatures and electric field based on neural network analysis, which provides a basis for the selection of PP material for HVDC capacitors of converter valves. The results show that, there is a small gap of key physical and chemical parameters between BOPP films corresponding to domestic ultra-pure pellets and imported ones, and the electric field strength and energy storage density corresponding to the charge-discharge efficiency of 90% at 85 ℃ are basically the same. The efficiency within 650 kV/mm under AC/DC superimposed voltage is maintained at the same level, thus showing a potential in the application in the practical projects of converter valves.