Mostly this song seems to be about drugs, but there are a some things that point to imperialism also.
Things that suggest drugs:
"China white" having been invented in 1976, close to 1977 (the first release of this song)
References to escape ("I could escape this feeling with my China Girl", "I could pretend that nothing really meant too much / When I look at my China Girl"), dependence ("I feel a wreck without my little China Girl", "I'm a mess without my little China Girl", "Wake up mornings, where's my little China Girl?"), and confusion ("I hear her heart beating, loud as thunder / Saw the stars crashing down", "I stumble into town", "Visions of swastikas in my head / Plans for everyone")
The last verse: "And when I get excited / My little China Girl says, / 'Oh baby, just you shut your mouth'/ She says, 'Shhh'" I'm not certain of this, having never taken heroin myself, but according to Wikipedia it causes feelings of relaxation or drowsiness (in addition to euphoria).
Things that suggest imperialism
The fourth and fifth verses, especially the fifth. The lines: "I'll give you television / I'll give you eyes of blue / I'll give you a man who wants to rule the world" in particular suggest the effect of 'Westernization' on other cultures.
Mostly this song seems to be about drugs, but there are a some things that point to imperialism also.
Things that suggest drugs:
Things that suggest imperialism