Morphological characteristics,flow cytometry and chromosome number were used to screen and identify tetraploidy plants from experimental materials through micropore culture,and excellent tetraploid lines were selected as parents to mate combinations randomly.And using various comparison tests,analysis of nutritional content and bolting tolerance to choose excellent combinations.It provides certain theoretical fundamental and practice methods of polyploid breeding in pakchoi.These results shows that:(1)76 tetraploid lines were identified from 232 DH(doubled haploid) group in pakchoi,and average of tetraploid ratio reached 32.76%,the highest one was ‘Inbred lines hybrid’.These tetraploid plants showed robust growth,dilatation of the main stem,flower organ huge,low selfing seeds setting rate and other characteristics.(2)11 tetraploid lines with high selfing seeds setting rate and excellent horticultural traits were selected as parents to mate 15 combinations randomly.And most hybrids were proved to have significant heterosis and higher yield compared with two diploid controls.(3)Contents of soluble sugar and soluble protein of tetraploid plants increased significantly than that of diploids.However,contents of organic acid and cellulose were obviously reduced.Moreover,most tetraploids had strong bolting resistance.So,it provides parent materials to create tetraploid hybrids which are high nutritional quality and bolting-tolerant.(4)Tetraploid hybrid combination ‘T11×T10’ has superior horticultural traits,strong heterosis,high nutritional quality and bolting resistance,also its yield was significantly higher than that of diploid controls ‘No.5’ and ‘No.9’ with 40.93% and 32.37%,respectively.So,it is a wonderful tetraploid hybrid in pakchoi with excellent commodity properties.