Orthotylus sophorae has become a serious pest for Sophora japonica in Linxia Prefecture of Gansu Province in recent years. The spatial distribution pattern of O. sophorae nymphs in S. japonica garden was determined by six spatial distribution pattern indices, and the assembling reasons were analyzed using Taylor's regression model (1961) and lwao's regression equation (1971). The results indicated that the aggregated distribution of O. sophorae nymphs in the field fits the negative binomial series (k_c=0.6169). The reason for the aggregation may be due to some environmental factors. On the basis of the distribution pattern, the optimal sampling number and sequential sampling table were calculated using lwao's method. The zero frequency model for the mean density estimation of O. sophorae nymphs was established on the basis of Gerrard's method (1970) as follows:x=1.7457(-lnP_o)^1.1119.