Based on the daily recorded date of annual hail from 1970 to 2001 and 500 hPa northern hemisphere, correlative analyses showed that annual hail days climate during summer in Northwest China at some extent had relation with winter circulation field and pole region circulation，westerly circulation and subtropical anticyclone. The contrast analysis  showed that polar vortex was lower in 500 hPa northern hemisphere in hail-more years, positive anomaly from mountain Ural  to Baikash lake, but negative anomaly from Yakutsk to Baikal lake, However, the conditions in hail-less periods and years were just adverse．A conceptual model for forecasting hail phenomena of the study region has been put forward.Results judged by the conceptual model are accordant to the results of multivariate regression analysis. It has proved by the  application that the conceptual model has considerable forecasting ability.