Frequency adjusting precision is an important performance indicator of miniaturized rubidium atomic clock (RAC) in some applications, such as the case in GPS disciplined RAC systems. This parameter is determined mainly by the resolution of digital phase-locked loop (PLL) in the frequency multiplier-synthesizer. To improve the frequency adjusting precision of a miniaturized high-performance high-stability RAC developed by our research group, the original RAC circuit scheme was improved by designing and implementing a new decimal frequency multiplier-synthesizer based on a high precision direct digital frequency synthesizer (DDS). Tests showed that this design achieved high precision frequency adjustment, while maintained the frequency stability as high as the original scheme.