Abstract: 【Objective】 To clarify the distribution of tobacco root-knot nematode species，the occurrence pattern and its mixed infestations with major root and stem diseases in major tobacco areas of Guizhou，and to provide scientific basis for the selection and breeding of root-knot nematode resistant tobacco varieties，tobacco production layout，and the formulation of integrated control strategies for root-knot nematode diseases in Guizhou. 【Method】 Using 98 samples of tobacco root-knot nematode infected roots collected from the main planting areas of 9 cities（prefecture）in Guizhou as materials，and the root-knot nematode species were identified by staining microscopy，morphological observation of the female perineal pattern，and molecular biology methods；the root-knot nematode incidence patterns（the initial infestation period of the root-knot nematode in the field，the life-history cycle，and the change pattern of the number of nematodes in the soil）were investigated using the dyeing and the Behmann funnel methods；and PCR technology was used to test Phytophthora nicotianae，Thielaviopsis basicola and Ralstonia solanacearum in root-knot nematode root samples. 【Result】 A total of 49 of the 98 samples were infested with root-knot nematodes，of which 21 samples（42.86%）were singly infested with Meloidogyne arenaria，the dominant population in Guizhou；and 11 samples（22.45%）were singly infested with M. incognita. Infestation rates of M. arenaria and M. incognita mixed population，M. arenaria and M. javanica mixed population were 30.61% and 2.04% respectively；there was 1 sample detected no root-knot nematode，which accounted for 2.04%. From the producing areas，Bijie City mainly had single infestation of M. arenaria and compound infestation of M. arenaria and M. incognita，Anshun City and Guiyang City had infestation by single M. arenaria，Liupanshui City had mainly single infestation of M. arenaria，Qiandongnan Prefecture and Qiannan Prefecture had single infestation of M. incognita and compound infestation of M. incognita and M. arenaria，Qianxinan mainly had single infestation of M. arenaria，Tongren City had single infestation of M. incognita and complex infestation of M. incognita and M. arenaria， Zunyi City mainly had compound infestation of M. arenaria and M. incognita. Rhizome diseases such as black shank， root black rot and bacterial wilt wee prone to mixed infection with root-knot nematodes，the detection rates of black shank pathogen，root black rot pathogen and bacterial wilt pathogen were 4.1%，6.1%，and 20.4%；the initial infestation period of root-knot nematode was 5-10 d after planting，and it took about 35 d to complete a life history cycle；the numbers of second instar of root-knot nematode per 100 g of soil at 15^th，20^th，25^th，30^th，35^th and 40^th d after transplanting were 96， 74，59，38，60，and 83 respectively，with a decreasing and increasing trend. 【Conclusion】 Root-knot nematode species in Guizhou tobacco area include M. incognita，M. arenaria，M. javanica，with M. arenaria as the dominant species；rootknot nematode is found in the main planting areas of 9 cities（prefecture）；the initial infestation period of root-knot nematode is 5-10 d after planting，and the life-history cycle lasts for about 35 d，and the number of second instar larva of rootknot nematode in soil around roots shows the tendency to decrease first and then increase gradually with the increase of infestation time；mixed infestation of different populations of root-knot nematode，as well as mixed with bacterial wilt， black shank and root black rot is common.