I want to delete flip particles by age in dop level instead of in sop level using delete node etc, so can I achieve that?

On the Source Volume node that you are emitting geometry from (assuming you are emitting), under the Particle Operation tab there is “Life Expectancy” you can set that (number of seconds) and turn on Flip Solver / Particle Motion / Behavior / Age Particles and Reap Particles

Solitude
On the Source Volume node that you are emitting geometry from (assuming you are emitting), under the Particle Operation tab there is “Life Expectancy” you can set that (number of seconds) and turn on Flip Solver / Particle Motion / Behavior / Age Particles and Reap Particles

Many thanks, it works! And if I want to group some particles in DOP, for example I want to group the particles speed higher than 0.5, and let them has high viscosity, how to do it in DOP?

There's a few ways. The easiest is that you can plug in the pop nodes (pop vop or pop wrange nodes (which are just encapsulated geometry vop / wrangle nodes or sop solvers) into the particle velocity input. It plugs straight into a pop solver, and you can do most of your stuff there. Or you can use a geometry vop or geometry wrangle node or sop solver however you wish to modify the attributes.

Solitude
There's a few ways. The easiest is that you can plug in the pop nodes (pop vop or pop wrange nodes (which are just encapsulated geometry vop / wrangle nodes or sop solvers) into the particle velocity input. It plugs straight into a pop solver, and you can do most of your stuff there. Or you can use a geometry vop or geometry wrangle node or sop solver however you wish to modify the attributes.

Aha, I see, thank you again!