In order to solve the problems on calculation of attachment energy Eatt of ionic crystals with complicated structures, several formulas derived according to the principle of PBC (Periodic Bond Chain) theory is presented. The appropriate computing programme has been worked out. The morphology of KTiOPO4 was deduced from the structure. The categories of the crystals faces have been distinguished by means of PBC theory. It was found that 100, 011 are F-forms, and 210, 010 are more important S-forms. The form of 001 is found to be K face. The calculation of Eatt for each form has been carried out, and it gives the relative importance of these faces. The results are in satisfactory agreement with observations. The calculating formulas and the programs can be used directly for calculating Eatt of other crystals belong to cubic, tetragonal and orthorhombic systems.