中小企业在经营活动中具有较强的灵活性，是市场经济活跃的重要元素，为扩大就业市场和提供丰富的产品做出了重要贡献。中小企业局限于企业规模、资金实力、技术、人才、经验等方面的因素，其危机抵御能力不足，许多原本经营良好的中小企业在遇到危机时瞬间陷入困境甚至破产。因而，国内外学者一直十分关注中小企业的发展，并中小企业危机进行了多方面的研究，其对中小企业危机防范的研究集中于财务、人力资源等职能危机预警和危机管理流程设计等方面。 鉴于中小企业危机抵御能力不足，应该在危机处于潜在阶段的时候对危机因素进行识别，并针对关键危机因素进行重点防范，有助于企业应对危机。本文运用约束理论（Theory of Constraints, TOC）思想，对中小企业的危机因素进行识别和评价，并在评价得分基础上，进行各评价指标评价的排序，从而识别企业的关键危机因素，进行有重点的危机防范，以提高企业应对危机的能力。文章在研究中遵循TOC约束因素识别原则提出中小企业存在的七方面的约束因素，在约束因素基础上提出了中小企业面对的资源、生产、通道、市场、业务、法规、环境七个方面的危机因素，并提出基于这七个方面的危机评价指标，提出了适合于中小企业的危机评价方法并在X商品混凝土公司进行实证分析，进一步提出中小企业危机防范方法。 中小企业的生存和竞争压力越来越大，在危机潜伏的时候能够有效识别并进行危机防范能够增强中小企业抵御风险的能力。基于TOC的中小企业危机防范方法在对TOC研究领域进行扩展的同时提出了中小企业危机防范的新方法，这种方法从危机的根源进行企业危机防范研究的方法在危机防范研究，实现企业危机的有效防范。

SMEs in business activities with strong flexibility is an important element of the economically active market for the expanding job market and provides a wealth of products to make an important contribution. Limited to small and medium scale enterprises, financial strength, technology, talent, experience and other factors, the lack of capacity to withstand the crisis, many well-run small and medium enterprises had a crisis moment in the face of hardship or even bankruptcy. Thus, domestic and foreign scholars have been very concerned about the development of SMEs and SMEs in many aspects of the crisis, its crisis prevention research focused on small and medium enterprises in the financial and human resources functions of the crisis early warning and crisis management process design and so on. Given the resilience of SMEs lack the crisis should be in a crisis stage at the time of the potential identification of risk factors and key risk factors for the key prevention, we must help companies deal with the crisis. In this paper, TOC thinking of SMEs to identify and evaluate risk factors, and the evaluation score, based on the sort of evaluation of each index, in order to identify the key risk factors for enterprises to carry out a focused crisis prevention, to improve the enterprise should crisis. Articles in the study followed the principles of TOC identified constraints proposed the existence of the seven aspects of SME constraints, the constraints facing SMEs is proposed based on the resources, production, channel, market, business, laws and regulations, the seven aspects of the environment risk factors, and make the crisis based on the seven aspects of evaluation, presented a crisis for small and medium enterprises in the X product evaluation and empirical analysis of concrete companies further proposed SME crisis prevention methods. The survival of SMEs and increasing competitive pressure, when the crisis can identify potential for crisis prevention and can enhance the ability of SMEs to resist risks. TOC-based crisis prevention approach of SMEs in the field of TOC at the same time extend the proposed new method of crisis prevention for SMEs, this method is carried out from the root of the crisis of corporate crisis prevention research methods in crisis prevention, crisis of enterprises Effective prevention.