Under the background of a same northeast cold vortex circulation, strong convective weather occurs in Shanxi for two consecutive days from 12 to 13 June 2016. On 12, it is a scattered convection, while it is a large-scale strong convection on 13. Based on multi-source data, the effects of the sub-synoptic scale system and its evolution on the environment and then on the structure of the storms are discussed through comparison. The results are as follows. (1) There are significant differences in the intensity and the structure between the two days’ storms. On 12, the convection is isolated and dispersed, and the echo intensity is less than 55 dBZ; while on 13, the strong convection is triggered by a quasi-linear convective storm that develops into a larger-scale bow echo, with the central echo intensity of 60 dBZ. (2) The key synoptic system of the process is the sub-synoptic scale vortex under the background of a cold vortex. On 12, the sub-synoptic scale low pressure disturbance begins to appear far away from Shanxi and does not have an effect there; on 13, it moves eastward and develops into a sub-synoptic scale cutoff vortex, and the surface cold front and 850-hPa shear line related to the vortex trigger the convection in the upper reaches of Shanxi. (3) On 12, the low-level specific humidity is low, and the vertical wind shear at 0-3 km is weak. On 13, the southerly water vapor transport in front of the vortex significantly humidifies the low layer, and with the superimposition of the dry cold air in the middle layer, an unstable stratification is formed. Under the influence of the vortex, the vertical wind shear at 0-3 km increases to 5.0×10^-3 s^-1. The convective storms triggered by the low-level cold front develop strongly and produce a gust front in the above environment, and the gust front drives the storms to form a squall line. The interaction between the cold pool and the wind shear at 0-3 km maintains the squall line. (4) The environmental factors conducive to the development of the squall line on 13 are closely related to the sub-synoptic scale cutoff vortex on the west of the northeast cold vortex. The sub-synoptic scale vortex is the key system for the formation and development of the squall line.