在编译器的设计中，静态单赋值形式（static single assignment form，通常简写为SSA form或是SSA）是中介码（IR，intermediate representation)的特性，每个变量仅被赋值一次。在原始的IR中，已存在的变量可被分割成许多不同的版本，在许多教科书当中通常会将旧的变量名称加上一个下标而成为新的变量名称，以至于标明每个变量及其不同版本。在SSA，UD链（use-define chain，赋值代表define，使用变量代表use）是非常明确，而且每个仅包含单一元素。

In compiler design, static single assignment form (often abbreviated as SSA form or simply SSA) is a property of an intermediate representation (IR), which requires that each variable is assigned exactly once, and every variable is defined before it is used. Existing variables in the original IR are split into versions, new variables typically indicated by the original name with a subscript in textbooks, so that every definition gets its own version. In SSA form, use-def chains are explicit and each contains a single element.