Return flight from Xi'An with single entry visa

Mohieddine, you best option is to have two separate, totally unrelated tickets. One from Osaka to Xi'an and another one from Xi'an to X country. By doing this, you have to be careful not to exceed 24 hours within the mainland China even for 1 minute. Having two separate tickets is important because like this the immigration authorities simply have to grant you a 24 hour free entry permit that allows you to exit the airport, have an overnight in hotel and in your case, to collect your luggage you will leave there at the end of your first stay in Xi'an.

Please, be careful about your second journey because if you have some other stop within mainland China after or before Xi'an, you have to be aware that even this stops are added to the entire time of your transit that should be covered by 24 hour visa free transit. Also, you have to be aware that you cannot use Urumqi airport as one of your stops if you intend to travel by using visa free scheme.

On more detail. It is very important detail that you book your overnight in Xi'an hotel in advance and to have a confirmation in hard copy with you upon your landing to Xi'an.

Thank you very much Zupan for your answer.
So The total duration ofthe transit must be less than 24h .
I've already booked my flights with separate airlines but I'll arrive to Xi'An on 27 sept at 17h20 and leave on 28 september at 20h20.
So it's more than 24H !!!
Do I have to take another flight from Osaka arriving later on september 27th (for exemple at 21h00) ?
Thank you

Exactly. You will need to change to a flight that arrives later so that your transit is under 24 hours.