Lyric, Free Verse
Of course, this poem was originally written in Chinese, so we're dealing with a translation here. But hey, given that we can't speak Chinese (we wish we could), we'll talk about the translation that's available to us.
First of all, we can describe this poem as a lyric work, because it's spoken by a first-person speaker, and the poem gives us an insight in the speaker's thoughts and feelings. After all, the poem is all about how the speaker's so in love with her hubby, and how much she misses him.
Form-wise, the poem is written in free verse, because, as we can see, there's no regular meter or regular rhyme scheme.
Let's take a few lines from the first stanza as an example:
When you, my lover, on a bamboo horse,
Came trotting in circles and throwing green plums.
We lived near together on a lane in Ch'ang-kan,
Both of us young and happy-hearted. (3-6)
As we can see, the lengths of these lines vary. There are ten syllables in line 3, eleven syllables in line 4, twelve syllables in the line 5, and nine syllables in line 6. There's also no regular stress in these lines. Because there is no regular meter or stress, we can safely say that the poem's written in free verse.
Again, it's important to keep in mind that this is the English translation of an ancient Chinese text, but we're still cool with this free verse form. Why? Well, think about it: this is a lonely wife essentially speaking to her missing husband. Based on their relationship, it seems totally the right choice to go free verse here, which lends the whole affair an informal, conversational tone. After all, when's the last time you spoke in sonnet form to your boyfriend or girlfriend?