Edit in JSFiddle

<div class="div1">div1</div>
<div class="div2">div2</div>
<div class="div3">
    <span class="span1">文字环绕了</span>
    div3
</div>
<div class="div4">div4</div>

.div1 {
    width: 100px;
    height: 30px;
    background-color: #000;
    color: #fff;
}
.div2 {
    float: left;
    width: 100px;
    height: 50px;
    background-color: red;
}
.div3 {
    width: 200px;
    height: 80px;
    background-color: blue;
}
.div4 {
    width: 300px;
    height: 70px;
    background-color: green;
}
.span1 {
    background-color: #ccc;
}