php artisan make:migration add_字段_to_表名_table --table=表名

use Illuminate\Database\Schema\Blueprint;

use Illuminate\Database\Migrations\Migration; 

class Alter表名DeletedAt extends Migration {

     public function up() {

        Schema::table('表名', function (Blueprint $table) {

                    $table->string('字段名')->default('默认值'); //默认值可以不加

        });

     }

     ...//其它方法

 }