Data from a long-term cancer morbidity registry and notification system were analyzed dynamically. A theoretical model of grey system was established based on time-series changes in cancer morbidities to predict its trend by the year of 2001 in Beijing. Results show cancer morbidities in Beijing will increase yearly from 1991 to 2001, and overall morbidity rate of malignant tumor will increase to 179.9/100,000 from 162.5/100,000. Proportions of malignant tumor in different sites will change greatly. Morbidities of lung cancer and breast cancer will increase rapidly, of liver and colon-rectal cancer shoes an increasing trend, too, of esophageal and cervical cancer will decline steadily, and of stomach cancer will begin to decline. All these facts laid a scientific basis for the study on cancer prevention and control.