首先要在AndroidManifest.xml中增加SD卡访问权限

<!-- 在SDCard中创建与删除文件权限 -->  
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>  
<!-- 往SDCard写入数据权限 -->  
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>   

private boolean ExistSDCard() {  
  if (android.os.Environment.getExternalStorageState().equals(  
    android.os.Environment.MEDIA_MOUNTED)) {  
   return true;  
  } else  
   return false;  
 }  

SD卡剩余空间

public long getSDFreeSize(){  
     //取得SD卡文件路径  
     File path = Environment.getExternalStorageDirectory();   
     StatFs sf = new StatFs(path.getPath());   
     //获取单个数据块的大小(Byte)  
     long blockSize = sf.getBlockSize();   
     //空闲的数据块的数量  
     long freeBlocks = sf.getAvailableBlocks();  
     //返回SD卡空闲大小  
     //return freeBlocks * blockSize;  //单位Byte  
     //return (freeBlocks * blockSize)/1024;   //单位KB  
     return (freeBlocks * blockSize)/1024 /1024; //单位MB  
   }   

public long getSDAllSize(){  
     //取得SD卡文件路径  
     File path = Environment.getExternalStorageDirectory();   
     StatFs sf = new StatFs(path.getPath());   
     //获取单个数据块的大小(Byte)  
     long blockSize = sf.getBlockSize();   
     //获取所有数据块数  
     long allBlocks = sf.getBlockCount();  
     //返回SD卡大小  
     //return allBlocks * blockSize; //单位Byte  
     //return (allBlocks * blockSize)/1024; //单位KB  
     return (allBlocks * blockSize)/1024/1024; //单位MB  
   }