In this paper, conventional meteorological data, AWS data and Doppler radar data are used to analyze the organization and formation mechanism, structure characteristics and evolution causation of a squall line in northern Henan on 29 July 2014. The results show that the squall line formed under the synoptic situation of pretrough. Before the convection, cold air invaded into the front of upperlevel trough and laid over the lowerlevel warm airflow in potential convection area to form a favorable mesoscale unstable stratification. The process can be divided into organizationevolution stage and regeneration stage. In the organizationevolution stage, eastmoving upperlevel trough and mesoscale topographic convergence line are the main trigger systems. The vertical circulation structure of the coexistence of front inflow and back outflow, the coexistence of lowerlevel convergence and upperlevel divergence, and the horizontal circulation structure of coexistence and derangement of ambient inflow and system outflow reflect the selforganization characteristics of the squall line. This positive feedback mechanism leads to develop and preserve for a long time. Moreover, convective cloud mergering of squall line and other storms is the important reason why its local organization structure boosts quickly. In regeneration stage, favorable thermodynamic condition and stratification characteristics, especially the vertical wind shear with stronger than moderate intensity are extremely advantageous to the development of organization structure of the squall line. Convective clouds merger where bow echo is intersected into squall line forming a mesoscale thunderstorm high near the ground. The convergence lifting motion formed by isallobaric wind and environment airflow in mesoscale wet region offered an important trigger mechanism for the regeneration of the squall line.