The invention provides plant fiber mulching paper and a preparation method thereof. The mulching paper has good indexes of wet tensile strength, tensile strength, tearing strength, bursting strength and water resistance. The mulching paper provided by the invention is prepared by utilizing plant fibers, can be degradable, and does not pollute the environment; tests in a field show that the mulching paper has good effects of preserving moisture and soil moisture and suppressing weeds, and the coverage period can reach 3-4 months; and the mulching paper can replace a current plastic film existing on a market, and solve the problem that the plastic film is difficult to degrade and pollute the environment.