The green jade pendant was a gift from Suyuan to her daughter, which Suyuan called Jing-mei’s "life importance." If you’re thinking, "What on earth does that mean?" then you’re not alone, Jing-mei is wondering the same thing. The pendant doesn't necessarily have just one meaning.
Suyuan gives the pendant to her daughter at a point when Jing-mei is feeling terrible about herself. Waverly has just humiliated Jing-mei in over dinner in front of their families, and top it all off, Jing-mei clearly doesn’t know a good crab when she sees one (gasp!). What this boils down to is that Jing-mei doesn’t have a strong eye for quality. So when she’s feeling bad about herself, and thinking that Waverly is better than her, it’s likely that she just can’t recognize her own value. This indicates that the pendant has something to do with Jing-mei’s self-worth, and clearly a lot to do with her life’s importance.
Another hint that the pendant has something to do with Jing-mei’s value is that she meets another guy who’s wearing a similar pendant. He says, "she [his mom] gave it to me after I got divorced. I guess my mother’s telling me I’m still worth something."
Suyuan also says that the pendant’s jade isn’t of very good quality, "This is young jade. It is very light color now, but if you wear it every day it will become more green." The jade could symbolize Jing-mei herself. She is still young and doesn’t have a good sense of her personal worth. But if she keeps acknowledging her value, she will improve with time because she has the ability to change. This is in contrast to Waverly, who is like a crab, "Always walking sideways, moving crooked. You [Jing-me] can make your legs go the other way." So Jing-mei has the ability to change and thus improve herself, whereas Waverly not so much.
Also on the note of changing, we know that the color of the jade will change and deepen over time. Well other things change too, like Jing-mei’s perception and understanding of the pendant. At first she sees it as a tacky necklace which she hides in her jewelry box. But after her mother dies, Jing-mei starts to wear it. It no longer is just an ugly necklace; now it reminds her of Suyuan. As Jing-mei seeks to find out what on earth this pendant is supposed to mean, she’s also seeking to grasp her own life’s importance, and trying to understand her mother. As Jing-mei learns more about herself and her mother, the meaning the pendant has for her deepens, just as the color of the jade will deepen.
Can we possibly gather anything more from this darn pendant? The answer is yes. We also think that Suyuan intended it to serve as a kind of connection between herself and her daughter. Suyuan says to Jing-mei, "See, I wore this on my skin, so when you put it on your skin, then you know my meaning." Jing-mei doesn’t begin to understand that her mom really loved her until after Suyuan's death – coincidentally also the point when Jing-mei started wearing the pedant every day.