The cultured free-living canohocElis of Porphyra haitannsis is common to be mixed with diatoms and its normal growth is thus affacted. In the experiment free-living conchocelis was cultured under the conditions of illuminating strength 1500 lux, for 10-12 hr/day and at normal temperature.Within the concentration extent, it was found that gernnaniuzn dioxide has no significant effert an the germination of Porphyro haitaninsis carpaspore，the growth of conchocelis .the maturing of conehosporangial cells and the formation of conchospore，but the chemical can effectively restrain the growth and relrroduetiun of attaching diatom and green algae. The poisoning mechanism of germanium dioxide to diatom and green algae is also discussed in this paper.