string b = li["审批人"].ToString();
SPFieldUserValueCollection userValues = li["审批人"] as SPFieldUserValueCollection;
//循环userValues获取里面的值
for (int i = 0; i < userValues.Count; i++)
{
spr.Text += spr.Text.Length > 0 ? userValues[i].LookupValue : userValues[i].LookupValue;
}