The invention relates to a water-based expandable fireproof steel structure 
coating and a preparation method thereof. The water-based expandable fireproof steel structure 
coating comprises the following components in 
mass percentage: 20-45% of 
coating matrix, 25-45% of nano-
flame retardant, 0.1-10% of 
flame-retardant synergist, 1-10% of filler, 0.2-5% of auxiliary agent and 5-30% of water. The preparation method of the water-based expandable fireproof steel structure coating comprises the following steps: firstly, preparing the nano-
flame retardant; secondly, adding a water-based 
epoxy emulsion, a water-based 
epoxy curing agent and a self-crosslinking 
silicone acrylic 
emulsion in the coating matrix into a stirring 
barrel, and stirring uniformly; thirdly, adding the nano-flame retardant, the flame-retardant synergist, the filler, the auxiliary agent and water, stirring for 10-30 minutes, adding a mixture into a ball 
grinding mil, 
grinding, checking whether the 
fineness of the coating meets a requirement, and if so, stopping 
grinding; fourthly, filtering the mixture with a filter screen, and separating grinding balls from the coating; and finally, filling the coating into a specified 
jar, discharging and barreling. The water-based expandable fireproof steel structure coating has a high 
expansion rate, has the fire endurance as long as 120 minutes and the coating thickens of 2 mm; and the water-based expandable fireproof steel structure coating is simple in preparation method, disposes 
solid wastes in the field of 
biomass power generation, is low in cost and wide in application and has significant economic and 
social benefits.