public static void main(String[] args) throws Exception {
        String str = "。。。fffffff现权力的监督与制约<img src=\"http://www.47re.jpg\" width=\"320\" height=\"140\"/>与执行，现权力的监督与制约--------<img src=\"http://www.4xx.jpg\" width=\"320\" height=\"140\"/>与执行，执行执行";
        str = str.replaceAll("(?is)<img(.*?)height=\"140\"","<img$1height=\"266\"");
        System.out.println(str);
    }

------解决方案--------------------

Java code

    String str = "\"。。。fffffff现权力的监督与制约<img src=\\\"http://www.47re.jpg\\\" width=\\\"320\\\" height=\\\"140\\\"/>与执行，现权力的监督与制约--------<img src=\\\"http://www.4xx.jpg\\\" width=\\\"320\\\" height=\\\"140\\\"/>与执行，执行执行\"。。。。。;";
        String newstr=null;
        newstr=str.replace("height=\\\"140\\\"","height=\\\"266\\\"");
        System.out.println(newstr);