Hi, sorry for bothering but I couldn't find a solution after I googling.

In case of dependency error, I reinstalled the ros melodic and gazebo 9 by

sudo apt remove ros-* sudo apt remove gazebo* sudo apt-get remove libgazebo* sudo apt-get autoremove sudo apt update sudo apt install ros-melodic-desktop-full

Then I

roslaunch gazebo_ros empty_world.launch

it failed to launch and output goes here

... logging to /home/zzhuang/.ros/log/4d7ea3cc-c2dd-11ea-adf9-107b444c6ede/roslaunch-zzhuang-computer-6608.log  
Checking log directory for disk usage. This may take a while.  
Press Ctrl-C to interrupt  
Done checking log file disk usage. Usage is <1GB.  

started roslaunch server http://192.168.0.35:39221/  

SUMMARY  
========

PARAMETERS
 * /gazebo/enable_ros_network: True
 * /rosdistro: melodic
 * /rosversion: 1.14.6

 * /use_sim_time: True

NODES
  /
    gazebo (gazebo_ros/gzserver)
    gazebo_gui (gazebo_ros/gzclient)

auto-starting new master
process[master]: started with pid [6618]
ROS_MASTER_URI=http://192.168.0.35:11311

setting /run_id to 4d7ea3cc-c2dd-11ea-adf9-107b444c6ede
process[rosout-1]: started with pid [6629]
started core service [/rosout]
process[gazebo-2]: started with pid [6635]
process[gazebo_gui-3]: started with pid [6641]
[ INFO] [1594406634.180853095]: Finished loading Gazebo ROS API Plugin.
[ INFO] [1594406634.181647545]: waitForService: Service [/gazebo/set_physics_properties] has not been advertised, waiting...
[ INFO] [1594406634.216561834]: Finished loading Gazebo ROS API Plugin.
[ INFO] [1594406634.217443493]: waitForService: Service [/gazebo_gui/set_physics_properties] has not been advertised, waiting...
[ INFO] [1594406634.345115625]: waitForService: Service [/gazebo/set_physics_properties] is now available.
[ INFO] [1594406634.358672854, 0.008000000]: Physics dynamic reconfigure ready.
terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::lock_error> >'
  what():  boost: mutex lock failed in pthread_mutex_lock: Invalid argument
Aborted (core dumped)
[gazebo_gui-3] process has died [pid 6641, exit code 134, cmd /opt/ros/melodic/lib/gazebo_ros/gzclient __name:=gazebo_gui __log:=/home/zzhuang/.ros/log/4d7ea3cc-c2dd-11ea-adf9-107b444c6ede/gazebo_gui-3.log].
log file: /home/zzhuang/.ros/log/4d7ea3cc-c2dd-11ea-adf9-107b444c6ede/gazebo_gui-3*.log

it stuck here and I have to ctrl+c to stop it.

Any idea to solve it? Much appreciate your help.