A burner comprising at least one burning unit, the burning unit comprising: a burner casing defining a first rich burning cavity, a second rich burning cavity and a lean burning cavity therein, wherein the burner casing is provided with a rich burning injection inlet in communication with the first rich burning cavity and the second rich burning cavity, a lean burning injection inlet in communication with the lean burning cavity, a first rich burning flame port in communication with the first rich burning cavity, a second rich burning flame port in communication with the second rich burning cavity and a lean burning opening in communication with the lean burning cavity thereon; and a flow-adjustment device, arranged in the lean burning opening and provided with a plurality of lean burning flame ports in communication with the lean burning cavity, wherein the first rich burning flame port and the second rich burning flame port are located at two sides of the plurality of lean burning flame ports respectively, a first blind passage and a second blind passage are defined between the flow-adjustment device and two side walls of the lean burning opening respectively, the first blind passage is located between the first rich burning flame port and the plurality of lean burning flame ports, and the second blind passage is located between the second rich burning flame port and the plurality of lean burning flame ports; wherein a maximum width of the first blind passage and a maximum width of the second blind passage are equal and denoted by W2, and a maximum width of the first rich burning flame port and a maximum width of the second rich burning flame port are equal and denoted by W1, wherein W2≥W1; wherein the burning unit further comprises: a rich burning nozzle configured to provide the rich burning injection inlet with the fuel gas and corresponding to the rich burning injector port; and a lean burning nozzle configured to provide the lean burning injection inlet with the fuel gas and corresponding to the lean burning injector port; characterized in that the maximum width of each lean burning flame port denoted by W3 and a height of the flow-adjustment device denoted by H satisfy: W3/H=0.03∼0.30 and in that a sectional area S3 of a gas jet port of the rich burning nozzle and a sectional area S4 of a gas jet port of the lean burning nozzle satisfy: S3/S4=0.25∼0.65. a burner casing defining a first rich burning cavity, a second rich burning cavity and a lean burning cavity therein, wherein the burner casing is provided with a rich burning injection inlet in communication with the first rich burning cavity and the second rich burning cavity, a lean burning injection inlet in communication with the lean burning cavity, a first rich burning flame port in communication with the first rich burning cavity, a second rich burning flame port in communication with the second rich burning cavity and a lean burning opening in communication with the lean burning cavity thereon; and a flow-adjustment device, arranged in the lean burning opening and provided with a plurality of lean burning flame ports in communication with the lean burning cavity, wherein the first rich burning flame port and the second rich burning flame port are located at two sides of the plurality of lean burning flame ports respectively, a first blind passage and a second blind passage are defined between the flow-adjustment device and two side walls of the lean burning opening respectively, the first blind passage is located between the first rich burning flame port and the plurality of lean burning flame ports, and the second blind passage is located between the second rich burning flame port and the plurality of lean burning flame ports; wherein a maximum width of the first blind passage and a maximum width of the second blind passage are equal and denoted by W2, and a maximum width of the first rich burning flame port and a maximum width of the second rich burning flame port are equal and denoted by W1, wherein W2≥W1; wherein the burning unit further comprises: a rich burning nozzle configured to provide the rich burning injection inlet with the fuel gas and corresponding to the rich burning injector port; and a lean burning nozzle configured to provide the lean burning injection inlet with the fuel gas and corresponding to the lean burning injector port; characterized in that a rich burning nozzle configured to provide the rich burning injection inlet with the fuel gas and corresponding to the rich burning injector port; and a lean burning nozzle configured to provide the lean burning injection inlet with the fuel gas and corresponding to the lean burning injector port; characterized in that the maximum width of each lean burning flame port denoted by W3 and a height of the flow-adjustment device denoted by H satisfy: W3/H=0.03∼0.30 and in that a sectional area S3 of a gas jet port of the rich burning nozzle and a sectional area S4 of a gas jet port of the lean burning nozzle satisfy: S3/S4=0.25∼0.65.