datePicker.datePickerMode = UIDatePickerModeDate;

UIDatePickerModeDate

The date picker displays months,days of the month,and years. The exact order of these items depends on the locale setting. An example
of this mode is [ November | 15 | 2007 ].

06001

http://developer.apple.com/library/ios/#documentation/uikit/reference/UIDatePicker_Class/Reference/UIDatePicker.html

您也可以从故事板设置模式更改:(参见屏幕截图)