see table 2

https://www.autismspeaks.org/what-autism/diagnosis/dsm-5-diagnostic-criteria

Thank you so much Joshua P Rosenzweig, but I still have some difficulty to differentiate between them. I hope I can find a clear cut point to be able to differentiate easily between them.  

The DSM 5 states that the 2 main symptoms in ASD are social/communication and restrictive behaviors. Language is no longer a main symptom. Thus, depending on where a person fits on these 2 symptoms, i.e., how much impairment is caused by these 2 main symptoms they will be "placed" on one of the 3 levels of severity, which indicates how much support is needed (substantial versus some).

Thank you dear Rita Obeid, and for you Joshua. Rita, this is a clear and helpful answer. But to more clarify my question, I am conducting a research and want to include the level of severity of ASD based on the DSM-V criteria as a variable. However, the centers from which I will recruit the sample do not use DSM-V criteria. So I have to do this classification independently. I hope to find clear differences between Levels 1, 2, &3. I will be happy if we find clear differences between them. Kind regards, Ahmad.

Then maybe you should find a scale or assessment measure that will objectively specify where your participants will lie on the scale in terms of severity. Try the M-CHAT questionnaire, that is the one right off the top of my head. I'm sure there are a lot. 

Thank you so much dear Rita. Although M-CHAT is only for toddlers, and may not assess exactly these levels, you have provided me with the solution. I will try to find a scale to get accurate and objective data. I will let you know when I find a tool... 

Also if you are doing this in developing countries check: Indian Scale for the Assessment of Autism. Thing is, this one was developed before the DSM 5. 

I am doing the research in Jordan (Arabic country), but any tool in English can be helpful.

Good question.  Adding a severity level to ASD and basing it on "supports intensity" is a huge bold step for the DSM. I will be curious to see how things evolve. I share your concern with the DSM-5 Table and its cell content and usefulness (validity) in guiding clinical judgement in determining a severity level for ASD.  It might be helpful to look at existing ASD diagnostic tools (e.g., ADOS, ADI-R) and how they can inform on the severity level. There is a good paper that looks at this using the ADOS (Hus, Vanessa, Katherine Gotham, and Catherine Lord. "Standardizing ADOS domain scores: Separating severity of social affect and restricted and repetitive behaviors." Journal of autism and developmental disorders 44.10 (2014): 2400-2412).  You might also want to consider looking at a standardized measure of supports intensity. For example, there is the Supports Intensity Scale (http://aaidd.org/publications/supports-intensity-scale) or Instrument for the Classification and Assessment of Support Needs (https://www.i-can.org.au/). Good luck with your work.

Thank you so much dear Prof. Marc J. Tassé for your valuable help. I will read these interesting resources, and hope to find the best solution.