Abstract:The host plant species and the harm extent of Chromatomyia horticola(Goureau) on outdoor vegetables were investigated in 2004 in Yangzhou City. There are 23 species of plants that belong to 6 families as hosts of C.horticola, in which Compositae, Cruciferae, Laguminosae and Cucurbitaceae are the main families. It occurs seriously on lettuce, cauliflower, pea, rape and horsebean. The hosts can be divided into four types: the most fitting host, fitting host, preferable host and secondary host. The oviposition of C.horticola on 8 kinds of hosts selected was checked under microscope, which had proved the investigation of host suitability and lettuce is the favorite host. According to the population dynamics of C.horticola on the outdoor vegetables, the host selectivity of C.horticola was analyzed under natural condition in this paper.