The invention discloses method for preparing concentrated pineapple juice. The production flow of the traditional concentrated pineapple juice comprises the following steps of: selecting raw materials, cleaning, cutting ends and removing peel, juicing, filtering, degassing, sterilizing, cooling, concentrating and bottling. The pineapple juice produced by adopting the method has the problems that appearance, colour and lustre are poor, the fruit juice yield is low and the quality is poor. In the method discloses by the invention, pineapple pulp is added with compound pectinase to be subjected to enzymolysis and squeezing, the juice yield is improved by 10-15%, and the ton consumption cost is reduced; after the compound pectinase is added for enzymolysis in the invention, the fruit juice and pulp are finer and smoother, the colour and lustre are better, and the appearance and flavour of the juice are improved; and by adopting the method disclosed by the invention, the liquidity of the juice is improved, the juice is easier to concentrate and evaporate, the energy consumption is reduced, the product quality is improved while the energy consumption is reduced, the cost is saved, and the market competitive power of the juice is improved.