The LSS series vertical water-tube oil (gas) steam boiler is a water-tube through-flow, vertical three-pass type. It adopts a fully automatic burner with excellent technical performance as the main combustion equipment. Through the automatic ignition function, it generates high-temperature flames, which enter the inner side of the dense drainage pipe inside the furnace from the top of the furnace tube, and then bend 180° upward at the lower part of the furnace tube to enter the interlayer between the furnace tube and the dense drainage pipe. It leaves the boiler through the upper flue opening of the furnace tube and is discharged into the atmosphere through the chimney. This furnace type has high heat exchange efficiency, small floor space, easy installation and high safety.