The source and the regularity of deviation when Erlang B formula or the corresponding channel utilization ratio formula is used in a limited user system is dissected, and the condition available of the two groups of formulas are pointed out.

• 由此不仅揭示了爱尔兰B公式和相应信道利用率公式用于有限用户系统时会有较大偏差的根源，剖析了偏差的规律性，而且得到了适用于有限用户多信道共用系统的修正公式。