Voltage stability analysis has become an important work for actual power grid planning and formulation of operation mode, the existing off-line software can not achieve voltage stability analysis and computation comprehensively. Based on the VSASP software, a new voltage stability assessment and control software is developed in this paper which can achieve the computation and visualization of fast contingency screening, determinstic assessment, probabilistic assessment, and preventive control based on continuous power flow and sensitivity analysis. The design of overall function modules framework, the realization theory of each function module, and the engineering application of the software are given. Application results of the software show that it is an effective tool for voltage stability analysis, and it can provide powerful technical support for voltage stability assessment and control of actual power grids.