Although many studies have focused on the influence of abiotic stress gradients on biological interactions, few studies explained the effects of both resource and non-resource stress gradients on the facilitation between species. We conducted a controlled experiment to study the effects of nutrient stress gradient on the interspecific relationship between Phormidium corium and Scenedesmus quadricauda under different calcium concentration. The results showed that when the calcium concentration was high, the change of interspecific relationship between the two algae along the nutrient stress gradient accorded with the SGH theory, that is, the competitive interaction changed into positive interaction. The reason for this phenomenon may be that in the stress environment, the population density is low and the encounter rate is low; secondly, facilitation may improve the harsh environment and make it more beneficial to the beneficiary species, which may enable the beneficiary species to survive in the environment that they could not survive before. When the calcium concentration was low, the change of interspecific relationship along resource stress was in line with the "Hump hypothesis", that is, facilitation reached the peak under medium resource stress. This phenomenon may be caused by the interaction between salt stress and nutrient. When calcium stress was high, it may not be conducive to the absorption of nutrients by algae, resulting in the fierce competition for limited resources in the harsh environment. While the facilitation effect may be strongest in the medium stress environment due to the relatively sufficient resource. These results emphasized the joint effects of various stress factors on interspecific relationships, especially the importance of non-resource stress in the study of community composition, pointed out a new direction for the study of facilitation, and provided theoretical guidance for the prevention and control of freshwater blooms.