Separation density is one of the most concerned operating parameters in gravity beneficiation.Although equal-errors cut point or distribution density is usually used as practical separation density in gravity beneficiation, the gravity separating process complexly affected by many kinds of factors is actually carried out at a fluctuant density; namely, the practical separation density is essentially a random variable.The studied results show that the equal-errors cut point is the mathematical expectation of this random variable, and the distribution density corresponds to the highest separation efficiency in the gravity separation process.This shows that the distribution density is the best working point of the gravity separation equipment under a particular operating condition.Therefore,in order to fully develop the function of the gravity separation equipment, the distribution density should be close to the theoretical separation density unlimitedly in the range of minimum fluctuation. Separation density is one of the most concerned operating parameters in gravity beneficiation .Although equal-errors cut point or distribution density is usually used as practical separation density in gravity beneficiation, the gravity separating process complexly affected by many kinds of factors is actually carried out at at a fluctuant density; namely, the practical separation density is essentially a random variable. the studied results show that the equal-errors cut point is the mathematical expectation of this random variable, and the distribution density corresponds to the highest separation efficiency in the gravity separation process.This shows that the distribution density is the best working point of the gravity separation equipment under a particular operating condition.Therefore, in order to fully develop the function of the gravity separation equipment, the distribution density should be close to the theoretical separation density unlimitedly in the range of minimum fluctuatio n.