Is it tough to apply for a CS PHD degree after several years in industry? Advantage:
Family support. My parents believed I should and are willing to offer some financial support. Actually they urged me.
I am currently in a big company doing relevant work and I did great.
I want to.
Disadvantage:
GPA is not good for me, 2.6 is pretty low for applying to a PhD. From what I know about my friends, those who applied for a PhD program right after undergraduate often had a much higher GPA(3.7+) than what I have.
Financial support from family may not be that much due to many reason.
I only have one published result in an irrelevant domain as third writer.
Details of my background:
I lived in China and want to apply for a PhD abroad.
Academic years
I was graduated from one of the best university in my country with a bachelor degree at 2015. I spent my academic years in my teacher's lab and competition.
I have ACM/ICPC regional bronze,  Meritorious Winner of ICM(Interdisciplinary Contest In Modeling) and National 2rd prize of MCM(Mathematical Contest In Modeling).
I cooperated with my teacher and senior, finished a paper about A* algorithm as third writer.
I would say putting efforts in competitions had some side effects to my GPA but I know excuse is pale and useless.
Industry Career
After 2017 I worked in a big company as a NLP engineer, later in 2018 I took lead of NLP team. My job allows me to follow most new discovery of academia. During the process of applying those state-of-the-art result to real world I earned much experience with huge dataset in many ways.
Goal:
I want to apply for CS PhD in NLP related domain.
In short:
I want to have apply for PhD and I'm worrying about my weak background.
Any advice/experience is appreciated
It sounds like you have many industry experiences that would look really good on a PhD application. To be blunt though, your GPA is pretty bad. If I was reviewing your application, I would worry that you are one of those students who is very capable, yet also not very focused. Experience has taught me that students who show immense promise (publications, awards, test scores), yet have really poor GPAs, rarely amount to much as graduate students in the modern system. 

While this may or may not describe you, students with low GPAs tend to also be the students who struggle to get to their teaching assistant duties on time and who cause administrative nightmares for the graduate committee. (E.g. failing all classes, but arguing that they should still be retained as a graduate student because they think they have a great dissertation). I'll admit that I personally only recommend PhD applicants below a 3.0 GPA for further review by the graduate admissions committee under very rare circumstances. (E.g. they overcame cancer or something). When I am reviewing applicants, low GPA is one of the easiest metrics to immediately discard an application. 

What to do:

Your industry experience should be emphasised as an indicator that your GPA is not reflective of what type of PhD student you will be. Your letters of recommendation need to speak to your work ethic and dedication specifically. These are the very best things you can do. I would be much more willing to overlook a poor GPA if everything else was very promising for the applicant (GRE, publications, letters of recommendation, industry experience, in person interviews). 

If you have external funding, some programs are much more willing to take you on. (If you are willing to pay the tuition, why would they turn you down? It's low risk for them). 

I would also consider applying for master programs as a means of "proving" yourself to PhD programs down the road.