ACAD SINICA,INST THEORET PHYS,BEIJING 100080,PEOPLES R CHINA
; ACAD SINICA,GRAD SCH,PHYS BRANCH,BEIJING 100039,PEOPLES R CHINA
; NANKAI UNIV,DEPT PHYS,TIANJIN 300071,PEOPLES R CHINA
; INST HIGH ENERGY PHYS,BEIJING 100039,PEOPLES R CHINA
A scheme, the so-called ''projection,'' for handling singularities in processes such as e(+)e(-) --> t(b) over bare$(-)<(nu)over bar> (or e(+)e(-) --> u(d) over bare$(-)<(nu)over bar>) is proposed. In the scheme, with the help of gauge invariance, the large power quantities (s/m(e)(2))(n) (n greater than or equal to 1; s --> infinity) are removed from the calculation totally, while in the usual schemes the large quantities appear and only will be canceled at last. The advantages of the scheme in numerical calculations are obvious; thus, we focus our discussions mainly on the advantages of the scheme in the special case where the absorptive part for some propagators relevant to the process could not be ignored, and a not satisfactory but widely adopted approximation is made; i.e., a finite constant ''width'' is introduced to approximate the absorptive part of the propagators phenomenologically even though QED gauge invariance is violated.