The sensitivity of the structure and strength of a squall line in the initial and early development stages to initial low-level humidity and environmental vertical wind shear is investigated in a two-dimensional idealized squall line simulation using the WRF model.The results of the sensitivity test of low-level humidity indicate that increasing low-level humidity is favorable for convective triggering and stronger convective systems.The increased squall line intensity and upward movement make it easier for new convective cells to form at the leading edge of the cold pool.The increased low-level humidity also leads to more precipitation,which raises the intensity of the cold pool.In addition,the results of the sensitivity test of low-level environmental vertical wind shear show that the convection is easier to become downshear tilted in the initial stage with stronger low-level environmental vertical wind shear,which is unfavorable for convective triggering.According to RKW theory,the interaction between cold pool and low-level environmental vertical wind shear is considered as an important mechanism for the development of squall lines.The cold pool is relatively weak during the early stages of squall line development,and with weaker low-level environmental vertical wind shear,it is easier for the convection to become upright,resulting in a stronger and deeper upward movement that is favorable to the strength of the squall line.