Hello,
I want to add a wave effect for ocean water but I don’t know the method.
I want this effect UE4 Ocean Water Shader - YouTube , I have tryed with world displacement but it works only on small surface.
Thanks you 
You should take a look at Nvidia’s waveworks solution… here is a whole thread about Nvidia Gameworks tools…
Nvidia Waveworks
waves like these are done through mathematics, one technique is called Gerstner waves. This has all the equations you need for them.
Ok but I’m novice and I don’t know how pass the equations to a mesh.
I used shape_plane for water, but when I resize it I need more details (more vertex) can I do that in UE4 ?
UE4 cant add geometry to mesh’s, you need to do that in a modeling program.
the math that describes how your water looks is built into the material, inside the material editor you can create any math equations you need for that particular material
waves are a pretty complex thing to create, without knowing the basics of material building in ue4. take a look at This and This to learn more
Have a look at the community ocean project. You’ll want to look at MF_Gerstner_Wave and MF_GerstnerWave_Set in Ocean/Materials and M_Ocean in Ocean/Materials/M_Ocean_Versions. It’s well commented so you can see how things are done.