How can I import particles that I just created in POP to SOP environment?
I used “popnet” sop but it did not work. Can anyone give me a hint?

If you've created your particle system under /part somewhere, then use the POP Merge SOP. In its POP Path parameter, click on the plus button and choose the particle network you want.

Yes! It works!

thanks

The POP Network SOP is almost like the POP Merge SOP except that you create your particle network *inside* it instead. Try it. In SOPs, put down a POP Network. Now hit the ‘i’ key to move into it. Now you're within POPs. Put down a Location POP and hit ‘u’ to move up. Make sure that the display (blue) flag is on the POP Network SOP. Now rewind your playbar to frame 1 and hit play.

The difference between them is where your pop network resides. In the POP Network case, notice that the path of your particle network is _not_ under /part. The POP Merge SOP on the other hand, allows you to merge in a particle network from elsewhere in the network of your hip file. Traditionally, pop networks could only reside under /part. However, in Houdini 6, the idea of “networks within networks” was added with these new “Manager” operators. I think that this is now the generally preferred workflow to use networks within networks.

Thanks Edward!
Both ways worked! (popnet and pop merge)