In order to study the effect of fluid viscosity on the flux during salt-finger double diffusion convection, an experimental tank with a moving baffle plate in the middle was used. The sugar-salt double-layer system was formed and was initially stationary. The experimental study for double diffusion convection flux was carried out by adjusting the mass fractions of the sugar and salt components to obtain a series of experimental conditions with the same density stability ratio and different fluid viscosities. The experimental results show that the influence of fluid viscosity on the flux of salt-finger double diffusion convection could not be ignored. Under the condition of the same double diffusion convection intensity, the greater the viscosity of the experimental fluids, the smaller the fluxes for the salt-finger double diffusion convection. When the kinematic viscosity coefficients of experimental fluids are less than 1.15 mm²/s, double diffusion convective fluxes of sugar and salt decrease with the increase of the fluid viscosities. When the mass fractions of the two component continue to increase, the viscosity of the salt solution still increases slowly while the viscosity of the sugar solution increases rapidly. The flux of sugar component between the stratified interface still decreases with the increase of the sugar solution viscosity. However, the flux of the salt component does not change. The Stern number is negatively correlated with the viscosity of the fluid.