explanation of the LED circuit
Is the circuit designed like that
  


It is reasonable to design a LED lighting circuit like that.


  
  and if one LED light is dead, then the whole parallel connection will be dead?
  


The entire series strand would be dead. Which could then lead to cascade failure of the other strands.


  
  is this circuit based on constant voltage or constant current?
  


It looks like it uses a capacitive drop power supply. These use the impedance of a capacitor to limit the amount of current into the circuit, so it is CC.


  
  the led light is about 9 w, so how much light lumen it could draw for these low power consumption led light?
  


It's not possible to know without a datasheet.