The invention belongs to the technical field of biomass pyrolysis and discloses a device for continuously pyrolyzing biomass all day by solar energy. The device comprises a condenser, a reactor, a low-temperature molten salt tank, a high-temperature molten salt tank and a product collector, wherein the condenser reflects energy of sunlight and transmits the energy to the reactor to increase the temperature, and to-be-pyrolyzed biomass enters the reactor for a pyrolytic reaction; a molten salt pipeline with two ends connected with the low-temperature molten salt tank and the high-temperature molten salt tank is arranged on a central shaft of the reactor, when the sunlight is sufficient, low-temperature molten salt enter the molten salt pipeline to absorb heat in the reactor to form high-temperature molten salt so as to store solar energy; when the sunlight is insufficient, high-temperature molten salt in the high-temperature molten salt releases heat for pyrolysis of biomass, so that the to-be-pyrolyzed biomass is pyrolyzed continuously all day. The biomass is heated by solar energy continuously all day to be subjected to pyrolytic reactions, and the device is green, environmentallyfriendly and pollution-free.