The invention discloses a method for acquiring sale data of shopping malls and supermarkets by monitoring a POS machine printing port. Problems of instability, complex procedures, revisable data and huge use cost of invoice during transport of sale data of current shopping malls and supermarkets to a tax bureau local end system are solved. The method comprises steps of 1) acquiring tax-control information which is downloaded by a tax bureau local end system and received by a server and downloading the tax-control information to a POS monitoring procedure so as to carry out the step 2; 2) receiving and downloading the tax-control information to a tax declaring disc by the POS monitoring procedure; finally 10) after the merchandise sales data passes through the CA authentication in the tax bureau local end system, the merchandise sales details are stored; and 11)-16) after invoice issuing passing through the CA authentication in the tax bureau local end system, invoice details are stored. The method is advantaged by convenient use, safe and reliable data, high stability and great reduction on use cost of invoice of a user.