$("#txt").on("click", function (event) {
    var $temp = $("<input>");
    $("body").append($temp);
    $temp.val($("#txt").html()).select();
    document.execCommand("copy");
    $temp.remove();
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

<div id="txt">复制这段文字</div>