The invention discloses a method for preparing mechanical beating grinding pulp on basis of a white poplar (GKT88 poplar). The method includes the following steps: step (1): peeling the white poplar, washing and degreasing the peeled white poplar, cutting the peeled white poplar into pieces, performing steaming, and adding water into the steamed pieces and performing one-stage squeezing defibering to obtain wood pulp; and step (2) performing a first stage mechanical pulping on the wood pulp, performing storing and naturally bleaching for a period after water mill, performing a second stage beating grinding, and storing the pulp for a period after beating grinding to obtain the mechanical beating grinding pulp which is bleached naturally, wherein the white poplar is a GKT88 poplar which is 4-5 years old, and the GKT88 poplar is obtained through domestication and propagation of a Taiwan white poplar seedling. According to the preparation method, chemical reagents are not required, industrial wastewater cannot be generated, and the preparation method is environment-friendly; the method can obtain qualified white pulp without a bleaching agent; and the yield of the obtained pulp can reach over 60%, and the heavy metal content is low.