Abstract: The synthesis and optimization of relational operations in hardware description languages are studied in the paper. It is pointed out that different synthesis methods should be used depending on the different situations in descriptions. Five methods are presented with algorithms and corresponding conditions to realize the relational operation, i.e., utilizing the standard comparison component, transforming relational operation to arithmetic operation, transforming argument argument relational operation to logic operations, transforming argument constant relational operation to logic operations, and synthesizing relational operation together with arithmetic operations. The combinational complexity of relational operations is also analyzed.