I am calcalculating electron temperature through boltzman plot method but slope is increasing and its value is positive when divided by -1/slope it becomes negative. Can this negative with temperature be ignored?
No, you can't just ignore the negative sign! Your Boltzmann plot shows a situation called population inversion and it is very uncommon to get this for so many states. The most probable explanation of the positive slope is that you have made some serious mistakes in your evaluation. Is it an emission spectrum that you are evaluating here?