Generally speaking, for primary and secondary school students, the best achievement is to do as many sit-ups as possible in two minutes. For college students and adults, the best grades may be higher.
The standard given in the National Fitness Guide is that adult women aged 20-24 need to do more than 36 in one minute to be excellent, 26-36 to be good, and 16-25 to pass.
It should be noted that the best performance of sit-ups is not the only criterion, and other factors should be combined to evaluate a person's physical quality and health.