The invention relates to equipment for producing liquid fertilizer through concentrated biogas slurry and a method for producing liquid fertilizer. The equipment comprises a storage tank, a complexing kettle, a synthesizing kettle, a stabilizing kettle, a smashing machine, a stirring tank, a colloid mill, a homogenizer, a fertilizer storage tank and a filling machine. The method for producing the liquid fertilizer mainly comprises the steps of adjusting acidity of the concentrated biogas slurry, removing heavy metal and then chelating to manufacture the liquid fertilizer favorable for crops to absorb. The liquid fertilizer is prepared from the following ingredients in a formula in parts by weight: 40 to 60 parts of concentrated biogas slurry, 2 to 6 parts of urea, 1 to 4 parts of ammonium nitrate, 4 to 12 parts of potassium nitrate, 0.2 to 0.5 part of calcium nitrate terahydrate, 3 to 6 parts of ammonium dihydrogen phosphate, 0.2 to 0.5 part of magnesium sulfate heptahydrate, 0.1 to 0.2 part of ferrous sulfate, 0.05 to 0.1 part of zinc sulfate, 0.05 to 0.08 part of borax, 0.005 to 0.1 part of ammonium molybdate, 0.05 to 0.1 part of manganese sulfate, 0.05 to 0.1 part of copper sulfate, 0.01 to 0.01 part of plant growth regulator, 0.005 to 0.01 part of chelating agent, 0.01 to 0.03 part of acid-base regulator, 0.001 to 0.001 part of deodorant, 0.005 to 0.01 part of sterilizing agent and 0.001 to 0.002 part of defoaming agent. The liquid fertilizer has the advantages of scientific and reasonable formula, simple manufacture and very obvious application effect.