The invention discloses an environment-friendly wall fireproof heat-preserving board and a preparation method thereof. The environment-friendly wall fireproof heat-preserving board is prepared from the following raw materials in parts by weight: 26-60 parts of straw powder, 0.2-3 parts of guanylurea phosphate, 0.1-1.2 parts of boric acid, 15-45 parts of magnesium oxide, 5-15 parts of magnesium chloride or magnesium sulfate, 1-30 parts of coal ash or diatomite in powder, 0-30 parts of crushed crude pearlite or leech powder, 0.1-0.5 part of a styrene-acrylic emulsion, 0.1-0.5 part of calcium lignosulphonate and 5-25 parts of tap water. The preparation method comprises the following steps: first, mixing straw powder, guanylurea phosphate, boric acid, magnesium oxide, coal ash or the diatomite in powder, crushed crude pearlite or leech powder and calcium lignosulphonate; then, adding magnesium chloride or magnesium sulfate, the styrene-acrylic emulsion and tap water; and after fully and uniformly stirring at normal temperature, putting in a template, rolling, maintaining and demoulding to prepare the wall fireproof heat-preserving board. The environment-friendly wall fireproof heat-preserving board has the characteristics of high compression and breaking strength, good moisture absorption, water adsorption, flame retardant and anti-freezing performances, small heat conductivity coefficient, no formaldehyde, environmental friendliness, fireproofness and heat preservation.