这是一个插件，可以满足您的需求：

插件：

(function($){

$.fn.autoGrowInput = function(o) {

    o = $.extend({
        maxWidth: 1000,
        minWidth: 0,
        comfortZone: 70
    }, o);

    this.filter('input:text').each(function(){

        var minWidth = o.minWidth || $(this).width(),
            val = '',
            input = $(this),
            testSubject = $('<tester/>').css({
                position: 'absolute',
                top: -9999,
                left: -9999,
                width: 'auto',
                fontSize: input.css('fontSize'),
                fontFamily: input.css('fontFamily'),
                fontWeight: input.css('fontWeight'),
                letterSpacing: input.css('letterSpacing'),
                whiteSpace: 'nowrap'
            }),
            check = function() {

                if (val === (val = input.val())) {return;}

                // Enter new content into testSubject
                var escaped = val.replace(/&/g, '&amp;').replace(/\s/g,' ').replace(/</g, '&lt;').replace(/>/g, '&gt;');
                testSubject.html(escaped);

                // Calculate new width + whether to change
                var testerWidth = testSubject.width(),
                    newWidth = (testerWidth + o.comfortZone) >= minWidth ? testerWidth + o.comfortZone : minWidth,
                    currentWidth = input.width(),
                    isValidWidthChange = (newWidth < currentWidth && newWidth >= minWidth)
                                         || (newWidth > minWidth && newWidth < o.maxWidth);

                // Animate width
                if (isValidWidthChange) {
                    input.width(newWidth);
                }

            };

        testSubject.insertAfter(input);

        $(this).bind('keyup keydown blur update', check);

    });

    return this;

};

})(jQuery);