Abstract: By applying theroies of fluid mechanics , thermodynamics and heat transfer , the paper elaborated programmingprinciples of two (2)application programs. One is SWLOSS for calculation of steam presure drop and hcat lossboth in injection of injecto's pipe string and surface pipelines. The other is PROLOS for calculation of fluid heat lossin producter during the production for heavy oil thermal recovery.
The programming principles of SWLOSS and PROLOS may ease the slcam injecion parameters preprocessing inthermal recovery numer ical moleling and conveniencrs some of post- -processing of mouleling results.They also can be extensively applied in sectors such as chemical engineering, water or oil thansporting and powersupply system,etc.

Key words: SWLOSS, PROLOS, Principle formula