假定土体重度对滑移线场没有影响，利用滑移线方法推导了考虑土体重度的条形基础极限承载力公式，公式中地基承载力系数 Nq，Nc和Nγ互不影响且Nq，Nc与已有结果相同。利用上限定理构造了滑移线场对应的速度场，求得了该速度场的上限解。结果表明滑移线解与上限解相同，这就证明了滑移线解是上限解答。将地基承载力系数Nγ同已有的其它成果进行了对比，并分析了此方法的误差来源，同时给出了修正公式。

Assuming the unit weight of soil has no influence on the slip-line field, the formula of bearing capacity of strip footing is got by slip-line method, in which the three bearing capacity factors Nq, Nc and Nγ don’t effect each other and Nq, Nc are the same as the published results. The upper-bound solution to bearing capacity of strip footing is deduced in the corresponding velocity field of strip footing to the slip-line field, which is the same as what is got using slip-line method. The slip-line result is accordingly proved to be the upper-bound solution. The bearing capacity factor Nγ is compared to those by other methods. The reasons that lead to the error by present method are analyzed and a modified formula is proposed.