The weakest bound electron potential model (WBEPM) theory is employed here to study the transition probability of N atom and ions. Some transition probabilities of allowed transitions are calculated. In the calculation, highly excited states are studied and spectral fine structure is also taken into consideration. Compared with the accepted values, results reported here are in excellent agreement with the accepted values, and the agreement is within experimental uncertainty, which is satisfying. (C) 2000 American Institute of Physics. [S0021-9606(00)30516-5].