With the development of high voltage direct current (HVDC) transmission technology,hybrid multi-infeed direct current transmission become a development trend.The mechanism of double bridge commutation failure of line commutated converter based high voltage direct current (LCC-HVDC) in hybrid double-infeed system is analysized.And the major influence factors of double bridge continuous and discontinuous commutation failure are distinguished.Through simulation under different AC system fault extent and trigger time,the effect of these two factors on commutation failure types is studied,and it is found that the AC voltage waveform distortion under slight fault is the main cause of double bridge discontinuous commutation failure.Then the control parameter of voltage source converter based high voltage direct current (VSC-HVDC) is optimized by Simplex algorithm to suppress double bridge discontinuous commutation failure of LCC-HVDC in slight fault.