Pyropia is an important marine crop and periodical dehydration could help kill fouling organisms during cultivation. However, our understanding regarding the effects of periodical dehydration on biomass yield and biochemical composition of Pyropia remains very lacking, particularly for thalli grown at different salinities. In this study, Pyropia yezoensis experiencing periodical dehydration or not was cultured at four levels of salinities (17, 25, 32, 39 psu) for 19 days. The highest growth rate was found at salinity 25 psu and lowest was at salinity 39 psu. Dehydration reduced relative growth rate at each salinity except for the insignificant decrease at 39 psu. Dehydration did not affect the maximal photochemical efficiency (Fv/Fm) and the highest salinity decreased it slightly. Dehydration induced more Chl a and carotenoids and highest Chl a content was found at salinity 39 psu. Dehydration did not affect phycoerythrin or phycocyanin content at salinities 25–39 psu but respectively increased them by 28% and 50% at salinity 17 psu. Dehydration did not affect content of any amino acid while salinity interacted with dehydration on most amino acids. The optimal salinity for the production of total amino acids (AA),essential AA, umami AA, and sweet AA was 25 psu for the thalli without dehydration; while it shifted to 17 psu for the thalli with dehydration. Dehydration and salinity interacted on content of the fatty acids C12, C18:1(n-9), C18:2(n-6), and C20:2(n-6). For the synthesis of eicosapentaenoic acid (EPA, C20:5(n-3)) and polyunsaturated fatty acids (PUFA) in thalli without dehydration, the optimal salinity was 39 psu, but the effect of salinity disappeared when thalli experienced periodical dehydration. These findings show the interactive effects of periodical dehydration and salinity on biomass yield and biochemical composition in P. yezoensis and provide insights into optimizing conditions for nori cultivation.