Biomass gas burner with adjustable flame length and using method thereof

The invention discloses a biomass gas burner with adjustable flame lengths. A mixing chamber is arranged in the center of inner burner blocks, a fuel gas source communicates with the left end of a fuel gas effuser through a fuel gas inlet pipe; the right end of the fuel gas effuser penetrates through a burner outer shell and extends into the mixing chamber; a fixed air cover sleeves the outer sideof the fuel gas effuser; a primary air channel is formed between the outer wall of the fuel gas effuser and the inner wall of the fixed air cover; a movable air cover is rotatably assembled on the outer side of the fixed air cover; a first air port and a second air port are correspondingly formed in overlapping parts of the fixed air cover and the movable air cover; the size of a opening formed by the first air port and the second air port is adjusted by a rotary movable air cover; one end of the primary air channel communicates with an air inlet pipe through the opening; the other end of theprimary air channel commu