I did an experiment, i replaced all meat with soy protein.one month later, muscle mass didn't change.does that mean soy doesn't lower testosterone?

Protein and T: Muscle mass is controlled by many factors. Dietary protein is one, but if you have adequate dietary protein, as you likely did originally, then more protein will not help. Soy protein does not lower T. That is a myth. If you're a normal male, your T is what it is, and is controlled by your pituitary. If you want more muscle, then you need to do resistance exercise training.

Confused: You sound confused about how the body works. There is very little relationship between what you eat and how your testosterone level is. Muscle mass will be mostly related to how much exercise you do, not whether you eat meat or soy protein.