The utility model relates to a variable diameter cover for extinguishing sparks, which belongs to a motor vehicle accessory. The utility model is suitable for extinguishing sparks for exhaust pipes of the motor vehicles which go into and out oil-bearing material storehouse storage areas, gas stations, etc. The utility model is composed of a cone variable diameter head, a connecting body, a spark extinguishing cover, etc. The utility model is characterized in that the variable diameter head is applied to the exhaust pipes of various motor vehicles; the casing of the cone variable diameter head and the connecting body are connected by large square teeth; the connecting body is fixed with the spark extinguishing cover through bolts, which is convenient for cleaning and smoke elimination. The utility model has the advantages of original design, reasonable structure, convenient manufacture, easy use, convenient assembly and disassembly, good sealing performance, wide practical scope and high spark extinguishing efficiency.