NOVELTY - Biogas fermentation-microalgae cultivation coupling method comprises: (i) carrying out biogas fermentation to obtain biogas and biogas slurry; (ii) filtering the biogas slurry to remove solid particles, then diluting as microalgae culture medium and loading into a microalgae culture reactor, passing carbon source into microalgae culture medium, culturing under light conditions, drying the biogas discharged from the reactor; (iii) harvesting microalgae and dehydrating to obtain algae mud and culture medium, extracting biological grease, phycocyanin and other high value-products from algae mud.    USE - Used as biogas fermentation-microalgae cultivation coupling method.    DETAILED DESCRIPTION - Biogas fermentation-microalgae cultivation coupling method comprises: (i) carrying out biogas fermentation to obtain biogas and biogas slurry; (ii) filtering the biogas slurry to remove solid particles, then diluting as microalgae culture medium, loading the culture medium into a microalgae culture reactor, passing carbon source into the microalgae culture medium via microalgae culture reactor bottom, culturing under light conditions, drying the biogas discharged from the reactor to remove water vapor; (iii) harvesting microalgae and dehydrating to obtain algae mud and culture medium, extracting biological grease, phycocyanin and other high value-products from algae mud, adding the remaining algae residue into culture medium after extraction and passing into biogas digester for biogas fermentation. An INDEPENDENT CLAIM is also included for biogas fermentation-microalgae cultivation coupling device, comprising a biogas fermentation system, a filtration system, a microalgae culture reactor, a biodiesel extractor and a dehumidifier, where the bottom of the biogas fermentation system through the biogas slurry pipeline is connected to the inlet of filtration system, the filtration system outlet is connected to the reactor via microalgae culture fluid conduit, the residue outlet of filter system through the pipeline is connected to biogas fermentation residue system. The upper portion of biogas fermentation system is provided with gas pipeline. The gas pipeline is set through the bottom of the microalgae culture reactor. The upper part of the reactor in microalgae culture is provided with the dehumidifier via purified methane pipeline. The dehumidifier is set to biogas device via by gas pipeline. The biodiesel export oil extraction residue extractor is connected to biogas fermentation system via algae residue pipeline. The upper part of the reactor is connected to microalgae culture water pipes.