@JaysonX 

Hey and Welcome

Sadly we would need some more information from you to be able to help.. 

What model of Deco do you have and how many nodes?  (2 / 3 / more)

Did you install the Deco App?  If so under settings there is a button for network optimistation, this will scan and change channel which could help you, it takes a few mins.    On the surface this would appear to be signal strenght between the Deco nodes, can you post a screenshot from the App of the affected node?  It should show signal and connection status

Hi  @Philbert , i have 3 deco m5. Below is the result of network optimization.

Below is the 3 device signal status. The one with slow connection is the "kitchen" node. But still the upload and download speed is too slow compare to other 2.

I place the "kitchen" node to the place where the main deco reside.

  @JaysonX 

Hey

On the screenshot below, if you select the Kitchen node it should tell you which node is its master.. and also how its connected (2.4 / 5ghz), along with an idea of the signal strength between the nodes.  If its connected to the wrong node (far away one and not near) then rebooting the deco should force it to reconnect again to a new master.

Post a screenshot if you have one