The invention discloses a water purification process, which is good in water purification effect, for a porphyra haitanensis seedling culture pond. The water purification process comprises the following steps: selecting underground water which is 9 to 11 meters below sand in March, and has the temperature of about 9 to 11 DEG C and the PH value of about 8 to 8.5, and settling the underground water in a settling tank for one week after the underground water is pumped, wherein harmful pests in water can disappear naturally in sunny days and the water utilization requirement of the porphyra haitanensis seedling culture pond can be met; and conveying the water subjected to settling purification in the settling tank into the porphyra haitanensis seedling culture pond during use. The water purification process has the advantages that the water obtained based on the water purification process for the porphyra haitanensis seedling culture pond does not contain harmful substances to porphyra haitanensis seedlings, so that the water purification effect is good, and the seedling culture requirement can be well met; stimulation and radiation of seedlings are facilitated; the survival rate of the seedlings is high, and the yield of nori is greatly increased; and development of the porphyra haitanensis industry to standardization and scale management is accelerated.