  We discuss the algorithm of the cutting rules of calculating the imaginary
part of physical amplitude and the optical theorem. We ameliorate the
conventional cutting rules to make it suitable for actual calculation and give
the right imaginary part of physical amplitude. The calculations of the
imaginary parts of several Feynman diagrams show that the ameliorated cutting
rules agrees with the conventional integral algorithm very well. The
investigation helps us to find that the optical theorem has severe
contradictions and problem, thus isn't right. Besides, the calculation of a
physical amplitude show that the ameliorated cutting rules keeps the physical
result gauge-parameter independent.
