Organic semiconductor lasers have shown great application potential in various fields, such as low-cost sensing, high-performance lighting and display, and lab-on-a-chip devices. Since the introduction of organic lasers in the 1960s, research on semiconductor laser devices has expanded to include various materials and structures. The organic laser has attracted much attention due to its wide range of emission spectrum and simple synthesis and processing. Researchers constantly pursue the goal of using organic semiconductors to fabricate low-threshold thin-film organic laser devices while retaining the characteristics of a wide luminescence spectrum of organic materials, simple and portable structure, and low cost. However, organic semiconductor lasers face challenges due to material stability under optical pumping and large optical losses under electrical pumping, making commercialization difficult. Many scholars have put great efforts into enhancing the performance of materials and optimizing the structure to minimize the threshold of organic semiconductor lasers. Herein, based on the basic principles of organic lasers, the main factors affecting the excitation threshold are summarized. A comprehensive analysis of the relevant factors and threshold conditions is performed, considering both positive and negative aspects of modal gain and modal loss that need to be addressed. We expect to provide a wide range of ideas for reducing the threshold of organic lasers and offer theoretical guidance for the practical industrial production of organic lasers.