Kraft method, as a chemical pulping method, is commonly used in the worldwide. Pulps producing by using this method have a lower pulp yield compared to semi-chemical and mechanical pulping methods. However, strength properties of kraft pulp are higher than those of pulps producing from other pulping methods. The many researchers have been tried to improve up to a point kraft pulp yield. The results of these researches revealed that the many factors such as chemical and anatomical structure of raw material, cooking conditions, chip quality, type and amount of additive significantly affect the kraft pulp yield. In this paper, factors affecting kraft pulp yield are discussed in detail.