Abstract: Angus beef cattles and Hereford beef cattles imported from Canada were superovulated by using CIDR and injecting FSH-PG in May to June and Augest to September 2004, which were grouped in random. Superovulation rate, average number of collected embryos, average available embryo number, available embryo rate, and A and B grade rate in available embryos were analyzed. The results indicated that under natural grazing conditions from May to June, the average number of collected embryos was 10.78, the average available embryo number was 5.75, and the average number of grade A embryos was 4.52 of Angus beef cattles after superovulated; Under the same conditions, the average number of collected embryos was 12.18, the average number of available embryos was 7.86, and the average number of grade A embryos was 6.5 of Hereford beef cattle. From Augest to September, the average number of collected embryos was 12.55, the average available embryo number was 8.14, and the number of grade A embryos was 6.62 of Angus beef cattles after superovulation. Meanwhile, the numbers of Hereford beef cattles were 10.25, 5.75, and 4.32, respectively. It is substantiated that suitable superovulation season to Hereford beef cattles is in Summer, and to Angus beef cattle is in Autumn.