Delta Airlines has San Jose SJC to Beijing via Seattle as low as $357 to $407 round trip for travel departures November to May 2018.
November and December fares are $397-$407 most dates up to Dec 4, then $357-$387 for much of January.
February only has a few dates under $400.
March and April are months with most dates at low fares in $300s.
May has about six dates from $382 to $412.
San Jose SJC – Seattle SEA – Beijing PEK – SEA – SJC