I plan to travel from Baku ( Azerbaijan) to Beijing by Azal Airlines then switch to Hainan Airlines to go to Tokyo(different airlines).

According to China's 24-hour visa-free transit policy, no Chinese visa is required. As long as you hold a valid Japanese visa, a confirmed onward ticket to Tokyo, and your stay in Beijing does not exceed 24 hours, you can transit visa-free. It is recommended to confirm in advance whether luggage is checked through directly to avoid needing to claim it and go through immigration.