A burner, comprising: at least one air pipe; at least one fuel pipe; a plurality of groups of mixing units (23, 24) disposed at a downstream end of the burner, wherein each of the plurality of groups of mixing units is arranged coaxially and adjacent to one another, and each group of mixing units comprises at least one fuel channel connected to the at least one fuel pipe and at least one air channel connected to the at least one air pipe, wherein an outlet (27, 61) of the at least one fuel channel and an outlet of the at least one air channel are angled relative to one another such that fuel flowing out of the outlet of the at least one fuel channel is mixed with air flowing out of the outlet of the at least one air channel, thereby achieving multiple-stage mixing of the air and the fuel, wherein each group of mixing units comprises a plurality of fuel channels, a plurality of air channels or a combination thereof, wherein the plurality of groups of mixing units comprises a first group of mixing units and a second group of mixing units, wherein the first group of mixing units and the second group of mixing units are arranged on a firing plate with three stages, and wherein the three stages (20, 21, 22) comprise a first stage, a second stage and a third stage, wherein the first group of mixing units comprises a first plurality of air channels arranged on the first stage of the firing plate and a first plurality of fuel channels arranged on the second stage of the firing plate, and a central longitudinal axis of each of the first plurality of air channels is angled relative to a central longitudinal axis of a corresponding one of the first plurality of fuel channels, and wherein the second group of mixing units comprises a second plurality of air channels arranged on the second stage of the firing plate and a second plurality of fuel channels arranged on the third stage of the firing plate, and a central longitudinal axis of each of the second plurality of air channels is angled relative to a central longitudinal axis of a corresponding one of the second plurality of fuel channels, and characterized in that each of the second plurality of air channels is arranged to be a passage passing through the first and second stages of the firing plate to connect with the at least one air pipe. at least one air pipe; at least one fuel pipe; a plurality of groups of mixing units (23, 24) disposed at a downstream end of the burner, wherein each of the plurality of groups of mixing units is arranged coaxially and adjacent to one another, and each group of mixing units comprises at least one fuel channel connected to the at least one fuel pipe and at least one air channel connected to the at least one air pipe, wherein an outlet (27, 61) of the at least one fuel channel and an outlet of the at least one air channel are angled relative to one another such that fuel flowing out of the outlet of the at least one fuel channel is mixed with air flowing out of the outlet of the at least one air channel, thereby achieving multiple-stage mixing of the air and the fuel, wherein each group of mixing units comprises a plurality of fuel channels, a plurality of air channels or a combination thereof, wherein the plurality of groups of mixing units comprises a first group of mixing units and a second group of mixing units, wherein the first group of mixing units and the second group of mixing units are arranged on a firing plate with three stages, and wherein the three stages (20, 21, 22) comprise a first stage, a second stage and a third stage, wherein the first group of mixing units comprises a first plurality of air channels arranged on the first stage of the firing plate and a first plurality of fuel channels arranged on the second stage of the firing plate, and a central longitudinal axis of each of the first plurality of air channels is angled relative to a central longitudinal axis of a corresponding one of the first plurality of fuel channels, and wherein the second group of mixing units comprises a second plurality of air channels arranged on the second stage of the firing plate and a second plurality of fuel channels arranged on the third stage of the firing plate, and a central longitudinal axis of each of the second plurality of air channels is angled relative to a central longitudinal axis of a corresponding one of the second plurality of fuel channels, and characterized in that each of the second plurality of air channels is arranged to be a passage passing through the first and second stages of the firing plate to connect with the at least one air pipe.