Effective task scheduling and deployment is hard to achieve in a Grid environment, where computing resources are heterogamous and shared between local and Grid users without a central control. Current scheduling systems, such as AppLeS, use NWS (Network Weather Service) for short-term estimation of resource availability and do not address the influence of the variation of resource availability in task scheduling. These inherent limitations prevent existing scheduling systems from working effectively to solve large-scale tasks in a Grid environment. Adopting APST (AppLeS Parameter Sweep Template) as the deployment environment, we have developed a task scheduling system for large-scale applications based on our recent results in performance prediction and task scheduling. Preliminary experimental results show that the newly developed system works well and is significantly more appropriate for large applications than existing systems.