顺序程序是指对机床及其相关设备进行逻辑控制的程序。对于电气自动化控制工程人员而言，广泛采用的控制流程是以顺序控制为基础的。而顺序程序的编制正是在这一基础上产生的一种用于PLC控制的编程方式。
数控系统先将程序转换成某种格式，CPU即可对其进行译码和运算处理。CPU高速读出存储在存储器中的每条指令，通过算术运算来执行程序。顺序程序的编制由编制梯形图以及其它PLC标准语言开始的，所谓梯形图可理解为CPU中算术运算的执行顺序(A sequential program is a procedure for the logic control of a machine tool and its related equipment. For the electrical automation control engineers, the widely used control process is based on the sequential control. The programming of sequential programs is a way of programming on this basis for PLC control.

The numerical control system converts the program into a certain format first, and the CPU can decode and deal with it. CPU reads every instruction stored in the memory at high speed and executes the program by arithmetic operations. Compiling sequential programs compiled by the ladder and began other standard PLC language, can be understood as the so-called ladder execution sequence arithmetic in CPU)