Abstract: Using equatorial wave modes and short-range forecast error samples of the global GRAPES (global/regional assimilation and prediction system) model, this study investigated the balance characteristics of mass and wind fields in the tropics and analyzed the problem of imposition of the Linear Balance Equation (LBE) in the tropics based on such characteristics. The results show the following: (1) Equatorial wave modes can explain a substantial fraction of the tropical forecast error variance, which ranges from 60%-80% in the mid-troposphere to more than 80% in the tropopause and lower stratosphere. (2) Only 30%-55% of the explained variance can be represented by the Equatorial Rossby wave (ER) modes, suggesting that contributions of other equatorial waves should not be ignored. (3) Based on the ER modes, introducing other equatorial waves, especially inertial-gravity and Kelvin wave modes, greatly reduces the coupling between the mass and wind. In this situation, the correlation between geopotential height and wind is close to zero in the mid-troposphere, and the correlation between geopotential height and zonal wind in the lower stratosphere is dominated by Kelvin wave modes. (4) The coupling between mass and wind was overestimated when using LBE in the tropics, because LBE mainly expresses the balance characteristics of the ER modes. Therefore, when LBE is used as the balance constraint, extra steps should be taken to reduce the fallacious correlation and allow for a decoupling of mass and wind in the tropics.