As dietary preferences diversify, aquatic foods remain a global staple, providing high-quality protein, essential fatty acids, and other essential nutrients. However, maintaining the quality and safety of seafood remains challenging. Salting is the primary postharvest processing method for the brown seaweed Undaria pinnatifida and can affect product quality and lead (Pb) accumulation. This study investigated changes in nutritional components, bioactive compounds, and Pb content throughout the harvest season and subsequent blanching and salting. Relationships among these variables were examined to identify suitable salting conditions. Samples were collected at nine 7-day intervals from the coastal waters of Dalian, China, and analyzed at the fresh, blanched, and salted stages. The maximum protein and alginate contents in fresh samples were 21.95% and 36.60% (dry weight), respectively, with a corresponding Pb content of 0.235 mg/kg. Principal component and Pearson correlation analyses showed that Pb accumulation was associated with protein and alginate contents. Salting with 40% salt for 48 h preserved favorable texture and color while maintaining Pb content below 0.35 mg/kg. These findings indicate that both harvest stage and processing affect nutritional quality and Pb levels. Although salting promotes Pb accumulation, controlling salt concentration and salting duration can limit this effect while preserving product quality. Salting with 40% salt for 48 h is therefore suggested as a suitable condition for producing salted U. pinnatifida with desirable texture, color, and Pb content. These findings provide a scientific basis for improving the quality and safety of salted brown algal products.