We presented an alternative computational method for determining the permitted LS spectral terms arising from l N electronic configurations. This method makes the direct calculation of LS terms possible. Using only basic algebra, we derived our theory from LS-coupling scheme and Pauli exclusion principle. As an application, we have performed the most complete set of calculations to date of the spectral terms arising from l N electronic configurations, and the representative results were shown. 1 As another application on deducing LS-coupling rules, for two equivalent electrons, we deduced the famous Even Rule; for three equivalent electrons, we derived a new simple rule. 31.10.+z, 71.70.Ej, 1 The table of LS terms for l N (l = 0-5) configurations is too long and over two pages, so we only present part of the result in this article.