共同诉讼为民事诉讼法学重点问题之一，一些结论颇受争议。通说采德、日“二分法”理论解释民诉法第55条，根据诉讼标的共同或同一种类区分必要共同诉讼和普通共同诉讼。“二分法”是大陆法系共同诉讼“类型化”标志之一，该划分以实定法规则为依据。但是民诉法第55条和比较法规则之间存在较大差异，用“二分法”解释民诉法第55条缺乏合理性。本文考察德、日共同诉讼“二分法”发展过程，在具体概念之外找到共同诉讼实质要点，将其中合理成分适用于我国共同诉讼制度构建。我国共同诉讼现存问题是规范的不适应性，即法律将共同诉讼“类型化”要件建立在诉讼标的这一单一化、偏实体性概念之上。本文提出在共同诉讼形成过程中重构共同诉讼“类型化”标准，并在诉讼标的和共同诉讼“类型化”之间定位其他合并事由。本文采取相对化诉讼标的理论，并扩张民诉法第55条含义，使其适应不同程序场景、容纳多种评价性要件。法院和当事人对程序主导权分配、促进纠纷一次性解决限度和提高司法效率等公共利益，都能通过诉讼标的概念将共同诉讼制度内在丰富价值转变可适用的法律规范。本文先将共同诉讼分为“当事人主导型”或“法院主导型”两类，在原告起诉、被告主张管辖权异议及法院依职权追加共同诉讼人等具体阶段，共同诉讼成立的识别要素不同、对应狭义或广义诉讼标的含义。除在程序进程中理解共同诉讼特点并对分类外，本文还结合不同维度法院追加当事人之事由，将共同诉讼进一步分为“实体原因型”共同诉讼、“效力拘束型”共同诉讼和“效率裁量型”共同诉讼。

The concepts and patterns of several parties participating in litigation is one of key issues and the relevant conclusions are quite controversial. It is generally believed that Article 55 of the Civil Procedural Law, which serves as the normative foundation for the system distinguishing between two types of joint action, according to the common object matter or the same kind of object matter of litigation, adopting from Germany and Japan’s necessary-common joint action framework. The framework is one of the symbols of the typology method of joint action in the civil law system and it is founded on the rules of positive law. However, Article 55 of the Civil Procedure Law and rules of comparative law differ significantly. Thus, it is inappropriate that we use the framework to interpret Article 55 of the Civil Procedure Law. The article first looks at how the typology of joint action developed in the comparative law circumstance, identifying the essence of joint action outside of specific concepts and then applies these counterparts or rationales to the formation of our joint action typology legal framework. The present issue in our law is that the rules are not flexible enough; in other words, the law attempts to use a single, substantive notion to fulfill the need of the court and parties and defines our joint action framework. The article aims to define the typology standard in the forming process of joint action, as well as find other justifications between the object matter of litigation and the typology of joint action framework. In order to allow Article 55 of Civil Procedure Law to be further construed, the article uses the variable theory to cast a new understanding and offer a research paradigm for expanding the meaning of Article 55 to adjust to various procedural scenarios and take account a range of evaluative factors. By applying the variable theory, the underlying principles such as the allocation of procedural dominant right between the court and parties, the promotion of one-time settlement of disputes, and improving the efficiency of litigation could be transformed and become applicable rules. The typology of joint action in the article is initially made into party-led and court-led groups relying on how it is formed and identified. In the specific stages of plaintiff’s filing a lawsuit, the defendant’s claim of jurisdictional objections and the court’s ex-officio addition of joint actions, the object matter of litigation adjusts its meaning from the narrow and broader sense, taking into account various aspects and considerations, the joint action can be divided into three categories, the “substantive cause” joint action, “judgment binding” joint action and the “discretionary efficiency” joint action.