Eleven aggregation indices were used to analyze the spatial pattern of rice infested by the rice gall midge Orscolia oryzae (Wood -Mason)in paddy field in different Mages from July to August, 1990 in Debao county. The pat-lern dynamics were tested by Fuzzy clustering method. At the same time,the sampling techniques were also studied. The results showed that the distribution patterns were aggregated as the infested plant density was not more than 3 plants per hill .and became uniform distribution as the plant density was more than 3 plants per hill. The basic components of distribution were colonies and the distribution of the basic components was aggregate. It could be divided into mo kinds of spatial patterns:the low density is in early stages,and the high density is in late stages. The optimum sampling position is the tillering plants of rice. The Iwao's sequential sampling model and improved Iwao's sequential sampling model of the infested plants are:Where.T'0(n) ,T'0(n) is upper limit and lower limit of accumulated sillvershool numbers in the process of sequential sampling respectively ;n is sequential sampling n umber ;t is t-value for certain significant level.