This paper presents SWIFT, a fast parametric flight mechanics evaluation program developed for aerodynamics and multidisciplinary design optimization. The program constructs a flight mechanics parametric method and uses Common Parametric Aircraft Configuration Schema (CPACS) format to facilitate data exchange with the optimization framework. SWIFT employs the vortex lattice method for rapid aerodynamic analysis and integrates empirical and semi-empirical approaches for flight mechanics evaluation to support rapid iterative computations in multidisciplinary optimization processes. SWIFT can evaluate flight performance including flight envelope, take-off/landing field length, range as well as stability characteristics including longitudinal and lateral static stability derivatives, short period mode, phugoid mode, roll mode, spiral mode and Dutch-roll mode. At the same time, SWIFT achieves computational accuracy that meets engineering requirements. A validation case of flight mechanics evaluation of ATR 42 reginal turboprop airline is presented in this paper to validate the accuracy and efficiency of SWIFT. By comparing SWIFT's simulation results—including stall speed, maximum flight speed, ceiling, take-off/landing distance, range, and cruise time—with actual flight data, the evaluation error of SWIFT is within 8%. The evaluation time for each flight performance is within 1 min. Results show that SWIFT can effectively balance computational efficiency with engineering accuracy requirements for flight mechanics analysis. This program provides a reliable and rapid flight mechanics evaluation solution for multidisciplinary optimization.