Understand why your lady cry...

Women are often cry more than men does. And they might have different reason to cry.
So, below article will lists down some common problem of why women cry.
Notice: the original article is taken from Asker.com which have posted by Mr. John M

Men cry more on logical reasons than women who are more emotionally / hormonally driven.

In the days leading up to her period, your girlfriend is likely to be more emotional than usual and may react to otherwise mundane things with tears. If you think she's overreacting, it's a good idea to comfort her anyway and treat her with some sympathy rather than mock her or completely disregard her feelings, regardless of your own take on the situation. In hindsight, she might eventually agree that she was making a big deal out of nothing, but in the moment there is no course of action but to play along. Make no mistake: Acknowledging that PMS is the cause of her feelings will lead to full-fledged anger and you'll be in for more than you ever bargained for.

Manipulation
Women learn pretty early on in life that men can get uncomfortable when faced with a crying woman, and will often do just about anything to stem the flow of tears. Whether it was a teacher who raised a bad grade after a sob story about a dead dog, or a dad who bought his little girl whatever she wanted so she would stop causing a scene at the mall -- a woman who has had this type of behavior reinforced in childhood will think nothing of trying the same tactics on a boyfriend in adulthood. Unfortunately, it can be tricky to differentiate the sincere tears from the ploy, especially early on in a relationship. When in doubt about her sincerity, removing yourself from the situation is probably the best call, and it’s the only one that guarantees you won't make the situation worse or end up caving in.

Sincere emotion
When it's not hormones or conniving manipulation, the reason for her tears is going to be a sincere and deeply felt emotion. Women respond emotionally to a lot of different situations, so it can be difficult to figure out exactly what's going on with her. The only way she'll be able to start to feel better, however, is if she feels heard and supported. Whether she's feeling hurt by someone (maybe even you) or is feeling frustrated or helpless in a situation she has no control over (perhaps trouble finding a new job), she may resort to tears as a release for her pent-up frustrations. In such a fragile state, your girlfriend isn't looking for a trite Mr. Fix-It synopsis of the matter, she's most likely just looking for someone who is willing to validate her feelings and give her the support she needs to solve things on her own.