Numerical flow-filed computations have been conducted around a projectile with a triangular ballute at Mach numbers of 0.3 ~ 0.9 and angles of attack of $0^{circ};{sim};30^{circ}$. The expansion shape of a triangular ballute has been determined from both the manufacturing dimensions and the wind tunnel test results. It has been assumed that the shape does not alter after the ballute has been expanded completely. The computed results showed a good agreement with the wind tunnel test results. A sensitivity analysis on the aerodynamic coefficients has been performed to evaluate the quantitative effects on the flight performance. Trajectory simulation results were also in good agreement with the flight test results.