Abstract: In view of the massive use of decimal arithmetic with different precisions in the digital signal processing application, a design of the arithmetic unit will be introduced.By analyzing the characteristics of the computation with Q15 format decimals, we add the multi-precision format to meet precision request in the multiply-accumulate process.At the same time, estimating the delay of executive components, we reasonably part the pipeline to implement the computation capability and reach high frequency.With the kernel of typical digital signal processing algorithms, we quantitatively analyze the performance of arithmetic unit.Under the TSMC 65nm technological condition, it runs at 500MHz.