The invention discloses a finned different-diameter gas spinning pre-mixing multipurpose combustor. A pre-combustion chamber defined by a pre-combustion chamber shell on the periphery of an outer secondary air sleeve of the combustor is included. The outer side of the pre-combustion chamber shell is sleeved with an over fire air sleeve. The tail end face of the pre-combustion chamber shell is circumferentially and symmetrically provided with outer expansion type over fire air spraying ports along the axis of a pre-combustion chamber outlet. Axial rotational flow blades are arranged at the outer secondary air sleeve outlet position and in an over fire air sleeve channel. When the finned different-diameter gas spinning pre-mixing multipurpose combustor serves as a gas combustor to be put into use, inner secondary air and outer secondary air are high-speed jet flow, gas is mixed with air and smoke in a hearth in a dispersion manner under the large-scale turbulence condition, and the NOx generating amount is effectively reduced. When the finned different-diameter gas spinning pre-mixing multipurpose combustor serves as a pulverized coal combustor to be put into use, under the joint action of the outer expansion type spraying ports formed in the tail end face of the pre-combustion chamber shell and the over fire air axial rotational flow blade, sprayed over fire air forms outer expansion type high-speed rotating jet flow around the axis of the pre-combustion chamber outlet, the gas-powder mixture entering the hearth is combusted under the MILD combustion condition, and the NOx generating amount is obviously reduced.