In 1973, Chang and Lee combined linear resolution with ordered resolution and proposed an ordered linear resolution, namely OL resolution. It greatly improves the efficiency and mechanicality of linearization. However, the OL resolution is not a complete resolution method. We propose a concept of strong reduction based on the reduction condition of the OL resolution. Strong reduction further restricts the reduction condition of ordered informational center clauses, and the strong reduction is a special case of the reduction condition. Based on strong reduction, we also put forward an improved OL resolution, called SOL resolution, and prove its completeness.