In Astrology, the Moon represents our feelings and emotions. Mars represents sex and aggression.
When your Moon aspects your partner’s Mars, or vice-versa, a sexual attraction is indicated. Traditionally, it has been thought that this aspect works best when the feminine partner is the Moon person, and the masculine person is the Mars person. This aspect indicates the union of female and male energies. It injects passion and an instinctual attraction to the relationship. It also makes for satisfying sex, as it blends emotional energies with physical passion. The Mars person is turned on by the Moon person, just as she is. Her basic femininity drives him absolutely wild.
On the downside, this aspect can lead to heated emotional arguments and hurt feelings. Particularly in the case of hard aspects between Moon and Mars, this aspect can result in hostility, violence, and volatility. The Moon person is likely to feel the Mars person is overly aggressive, while the Mars person feels the Moon person is moody and insecure. The Mars person easily offends the Moon person, while the Mars person may feel the Moon person is too touchy and sensitive. Mars may try to change the Moon person, and may become impatient with her.
My last relationship featured a double Moon-Mars synastry aspect (square and opposition). His Libra Mars irritated my Moon in Aries; he was very indecisive, which tended to grate on my nerves. My Mars in Aquarius squared his Moon in Taurus; I found him a bit judgmental, but I opened his mind to a variety of sexual experiences he had never indulged in before.
The harmonious aspects (sextile and trine) are much easier to handle for both parties. In this case, the Moon person has a soothing, calming effect on the Mars person, while the Mars person energizes the Moon person. It also enhances cooperation and sexual compatibility.