The invention provides black masterbatch, prepared from, by weight, 28-62 parts of carbon dioxide-propylene oxide copolymer, 20-40 parts of poly(carbonate-ether)diol, 15-30 parts of carbon black, 0.5-2 parts of an end-capping agent, and 1-3 parts of a lubricant. The carbon dioxide-propylene oxide copolymer and the poly(carbonate-ether)diol are used as bases, and the carbon black masterbatch is well compatible with a biodegradable film. The poly(carbonate-ether)diol increases mobility such that carbon black can still be squeezed out smoothly under high addition and is good in precipitation resistance. The invention also provides a preparation method of the black masterbatch and black mulch. Experimental results show that the addition of the black masterbatch is up to 30%; the black mulch 5 Mum in thickness made with the black masterbatch has tensile strength of 232.2 MPa, elongation of 477% and light transmitivity of 4.6%.