您将需要一次将一个值添加到数组中。

var parameters = new string[items.Length];
var cmd = new SqlCommand();
for (int i = 0; i < items.Length; i++)
{
    parameters[i] = string.Format("@Age{0}", i);
    cmd.Parameters.AddWithValue(parameters[i], items[i]);
}

cmd.CommandText = string.Format("SELECT * from TableA WHERE Age IN ({0})", string.Join(", ", parameters));
cmd.Connection = new SqlConnection(connStr);

更新：
这是一个扩展且可重用的解决方案，该解决方案使用了Adam的答案及其建议的编辑方式。我对其进行了一些改进，并使其成为一种扩展方法，以使其更易于调用。

public static class SqlCommandExt
{

    /// <summary>
    /// This will add an array of parameters to a SqlCommand. This is used for an IN statement.
    /// Use the returned value for the IN part of your SQL call. (i.e. SELECT * FROM table WHERE field IN ({paramNameRoot}))
    /// </summary>
    /// <param name="cmd">The SqlCommand object to add parameters to.</param>
    /// <param name="paramNameRoot">What the parameter should be named followed by a unique value for each value. This value surrounded by {} in the CommandText will be replaced.</param>
    /// <param name="values">The array of strings that need to be added as parameters.</param>
    /// <param name="dbType">One of the System.Data.SqlDbType values. If null, determines type based on T.</param>
    /// <param name="size">The maximum size, in bytes, of the data within the column. The default value is inferred from the parameter value.</param>
    public static SqlParameter[] AddArrayParameters<T>(this SqlCommand cmd, string paramNameRoot, IEnumerable<T> values, SqlDbType? dbType = null, int? size = null)
    {
        /* An array cannot be simply added as a parameter to a SqlCommand so we need to loop through things and add it manually. 
         * Each item in the array will end up being it's own SqlParameter so the return value for this must be used as part of the
         * IN statement in the CommandText.
         */
        var parameters = new List<SqlParameter>();
        var parameterNames = new List<string>();
        var paramNbr = 1;
        foreach (var value in values)
        {
            var paramName = string.Format("@{0}{1}", paramNameRoot, paramNbr++);
            parameterNames.Add(paramName);
            SqlParameter p = new SqlParameter(paramName, value);
            if (dbType.HasValue)
                p.SqlDbType = dbType.Value;
            if (size.HasValue)
                p.Size = size.Value;
            cmd.Parameters.Add(p);
            parameters.Add(p);
        }

        cmd.CommandText = cmd.CommandText.Replace("{" + paramNameRoot + "}", string.Join(",", parameterNames));

        return parameters.ToArray();
    }

}

像这样

var cmd = new SqlCommand("SELECT * FROM TableA WHERE Age IN ({Age})");
cmd.AddArrayParameters("Age", new int[] { 1, 2, 3 });

请注意，sql语句中的“
{Age}”与我们要发送给AddArrayParameters的参数名称相同。AddArrayParameters将用正确的参数替换该值。