I'm new to VR development, I am a bit confused what's the differnce and the relationship between Cardboard Sdk and Oculus Sdk, if I want to develop an App which can play 360 VR video or photos, then which one is better I should to choose?
By Oculus SDK, I assume you mean the mobile SDK for GearVR since you mention cardboard. If you're talking about the SDK for PC, then the question is Oculus vs SteamVR vs OpenVR vs Morpheus :)
The major choice for which to develop for I think probably comes down to what your timeline and audience is.
GearVR is the best quality device out there right now and it is SIGNIFICANTLY more polished than cardboard, and it requires specific expensive hardware (Note 4 or S6, soon the Note 5). It has a store that people are buying things off of (even if it's not much yet). But since GearVR apps in development need to be signed, you will only have an audience if you can commit to at least a demo that will be accepted on the Samsung store. (the alternative is to have every user use the developer-signing system, which means you'll get tens of people instead of thousands to see it probably)
Cardboard is a very short-term experience. There are no head-straps on cardboard for a reason - it's intended to be something you hold up for only a minute or two at a time. Most of the audience is people interested in tech demos, but many more people will be able to try out your app. Google is working on stuff behind the scenes, so there may be more meat on it in the future - a non-cardboard VR device I've heard rumors of, and they're pushing cardboard pretty hard for classroom experiences. And in a couple years, every phone MIGHT have sensors good enough to give a GearVR-level experience.
Both SDKs will give you the basic two-eye 3d stereo rendering framework. Oculus' is a little more fleshed out with some built in scene loading (it converts from FBX format which is made by MODO, which is expensive) and a UI library (I'm not very happy with it though).
Either way, most of the work you do will likely be independent of the SDK you use, so I don't think you'll be boxing yourself in whichever one you choose.