Based on the S-band dual polarization Doppler weather radar data of Jinan, combined with sounding and surface meteorological observation data, the evolution characteristics of two severe storms, occurred in Shandong province on 30 June and 9 July 2021, are analyzed. The results show that: Two severe storms both occurred in the cold vortex background situation, and the trigger mechanism and storm morphological structures were different. The supercell storm was triggered by the gust front on July 9, and the strong squall line was triggered by the weak cold front on June 30. The continuous stimulating, merging and developing of new convective cells resulted in two severe storms lasting for a long time. The stimulation of the new cells in the intersection area of the west side of the supercell storm and the gust front guided the storm to propagate westward, so the right side of the supercell storm is the key area. Continuous stimulation of convective cells ahead of the east side of the strong squall line guide the storm to rapidly propagate and move forward, and evolve into bow echoes, so the key area is in front of the storm on the left side. At the initial moment of the new cells (30-44dBZ), the differential reflectivity (Z_DR) column height is around the environmental -10℃ level, containing sparse and medium sized liquid drops. With the rapid development of new cells, Z_DR columns can extend to -20 ℃ level or even higher, containing large liquid raindrops or melted small ice particles. The main characteristic of the cell merging is the merging of Z_DR columns, that is, the merging of the updraft zones. After mergence, the width or height of Z_DR columns and the values of Z_DR and K_DP will increase , the size and concentration of liquid particles in the strong upward airflow zone will increase obviously. There are extra large drops exceeding 5mm or melted ice particles inside the Z_DR column with the Z_DR values of 5-6 dB. The new cells have strong upward airflow at its initial moment, and then the intensity of the upward airflow rapidly strengthens with liquid particles appearing at the -20 ℃ layer or even higher heights. After the mergence , the intensity of the updraft becomes stronger, and extra large raindrops or ice phase particles equivalent to extra large raindrops will appear above the height of the 0 ℃ layer .