In the laser radar (Lidar) application scenarios,high power vertical cavity surface emitting laser (VCSEL) attractes more and more attention.However,in the long wavelength band,such as 1 550 nm lasers,there are problems such as unsatisfactory output power and low power conversion efficiency.At present,multi-junction VCSEL is the key technology to obtain high power,high power conversion efficiency (PCE),high optical power density and high slope efficiency (SE).This paper combines 1 550 nm VCSEL and multi-junction technology,which aims to design a high power 1 550 nm device.Finally,1 550 nm multi-junction (1—4) VCSEL devices with different diameters (15 μm,20 μm,30 μm,50 μm,100 μm) are successfully designed and simulated.By comparing the output power of devices with different parameters,it is found that the output power of devices increases with the junctions and diameter,and the maximum power can reach 2 217 mW(4 juctions,100 μm,VCSEL).And the results show that the output characteristics of 30 μm VCSEL are relatively good:the SE of single junction structure is better than that of 50 μm and 100 μm,is 0.39 W/A,the SE of multi-junction structure is better than those of 15 μm and 20 μm,is 0.89 W/A,is 1.55 W/A and 1.79 W/A respectively.Finally,the PCE and far field distribution of 30 μm VCSEL are analyzed,the paper found that PCE significantly increases with the increase of junctions,up to 40.4% of three junctions,only 1 A driving current,this is 6.2 times the PCE of single junction device.The power output of three junctions VCSEL is up to 1 549 mW,and there is almost no difference in beam divergence between single junction and multi-junction devices,is about 5°.These results provide a good device research basis for the application of 1 550 nm VCSEL as Lidar system and 3D sensing.