The invention relates to a cyanide-free chemical method for plating thick gold, particularly a double-tank method for continuously plating thick gold with cyanide-free chemical gold plating solutions. The method comprises the following steps: 1) immersing a substrate in a first cyanide-free chemical gold plating solution, and carrying out replacement gold plating to deposit a thin gold layer, wherein the thickness of the obtained gold film is 0.02-0.08 mu m; and 2) transferring the product obtained in the step 1) into a second cyanide-free chemical gold plating solution, and carrying out reduction-type chemical gold plating to deposit a thick gold layer, wherein the thickness of the obtained gold film is up to 0.3-2 mu m. The gold plating has the advantages of favorable binding force with the substrate, golden appearance and fine and compact crystals. The purity of the gold layer is 100%; and when the gold layer is subjected to welding, no black tray phenomenon is generated. The cyanide-free chemical gold plating solutions have the stability for practical application. The invention can solve the problem of thin gold layer in the replacement gold plating technique, and the problems of high pollution tendency, cyanide containing and the like in the plating solution in the reduction-type chemical gold plating technique.