During tethered balloon preliminary design, the residual buoyancy choosing directly affect the parameter design of envelop and ballonet such as volume. Inappropriate residual choosing will leading to project cost increasing or cannot achieve equilibrium characteristic. This paper analyzed and calculated the equilibrium characteristic of the same tethered balloon with different buoyancy, and two tethered balloon with different volume at the equal residual buoyancy. The result shows residual buoyancy has significant impact on tethered balloon static equilibrium characteristic, especially for small volume tethered balloon. The residual buoyancy should be serious considered during preliminary design. While considering helium input magnitude, the appropriate residual buoyancy choosing will increase economic characteristic for big volume tethered balloon.