@Lakotaubp @advocatux Thanks!
I followed jamieweb's way to modify ubports-installer(https://www.jamieweb.net/blog/installing-ubports-ubuntu-touch-on-the-meizu-mx4-ubuntu-edition/#fixing-the-failed-remote-unknown-command-error) and got UT installed on my MX4 finally!
This latest method is proved to work and should be topped.
Many thanks to @jamieweb and @AlainW94!

@Lakotaubp @advocatux Thanks!
I followed jamieweb's way to modify ubports-installer(https://www.jamieweb.net/blog/installing-ubports-ubuntu-touch-on-the-meizu-mx4-ubuntu-edition/#fixing-the-failed-remote-unknown-command-error) and got UT installed on my MX4 finally!
This latest method is proved to work and should be topped.
Many thanks to @jamieweb and @AlainW94!

Still can't access it. Maybe I'm blocked indeed.
So does https://imgur.com/k6mHCjX.

@advocatux I uninstalled the modemmanager and still failed to flash my phone with the same error.
BTW, I can't open https://web.archive.org/web/20180118130643/http://www.mibqyyo.com/en-articles/2015/09/16/ubuntu-android-installation-process-for-bq-aquaris-e4-5-and-e5/

Thanks anyway!

I tried to use SP Flash Tool(v5.1612) to flash my Meizu MX4 (Flyme edition)
and got the following error.

Connecting to BROM...
Scanning USB port...
Search usb, timeout set as 3600000 ms
add@/devices/pci0000:00/0000:00:14.0/usb1/1-4

add@/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0

add@/devices/pci0000:00/0000:00:14.0/usb1/1-4/1-4:1.0/tty/ttyACM0

vid is 0e8d

device vid = 0e8d

pid is 0003

device pid = 0003

com portName is: /dev/ttyACM0

Total wait time = -1559544040.000000
USB port is obtained. path name(/dev/ttyACM0), port name(/dev/ttyACM0)
USB port detected: /dev/ttyACM0
BROM connected
Downloading & Connecting to DA...
COM port is open. Trying to sync with the target...
Failed to Connect DA: S_BROM_DOWNLOAD_DA_FAIL
Disconnect!
BROM Exception! ( BROM ERROR : S_BROM_DOWNLOAD_DA_FAIL (2004)

[H/W] Fail to download DA to baseband chip's internal SRAM! 
[HINT]:
1. There's an cable communication problem between FlashTool and BootROM.
2. Target might be shutdown unexpectedly or target lost power supply.
[ACTION]
1. Try again.
2. Proceed H/W checking in download cable and target side com port.
3. Monitor if power-drop occured in target side.)((ConnectDA,../../../flashtool/Conn/Connection.cpp,127))

What should I do now?
Any help would be greatly appreciated!