With the construetion of satellite-ground integrated communication network,the collaboration between space bonemicrosatellites and ground stations can achieve global coverage and high-speed transmission of signals. This new communication modeputs forward higher requirements for the stability and accuracy of the clock, which cannot be satisfied by using crystal oscillator.Combining with the requirements of satellite-ground integrated communication network and the excellent short-term frequency stability ofrubidium atomic frequency standard(RAFS), the miniaturization design of RAFS is carried out by using phase-locked microwavegeneration, direct digital frequency synthesizer, preamplifier, phase sensitive detection and TEon mode magnetron microwave cavity. The100 MHz phase-locked output function is added to RAFS to meet the requirements of communication payload on clock frequency as well.Performance analysis exhibits that the miniaturized low phase noise space borne RAFS has the characteristics of high stability, low phasenoise and wide operating temperature range. The weight of the product is 1.8 kg, the steady-state power consumption is 22 W, thefrequency slability of 100 MHz signal is σry(π)≤3×10⁻¹²x-¹²(1s≤r≤10000 s) and the phase noise @1 MHz is -162 dBc/Hz. TheRAFS can operate stably in orbit for a long time, which can be used as the clock source of communication satellite payload.