To meet the urgent requirement of new-generation millimeter phased array antenna for the light, thin and small T/R module technology, this paper proposes a Ka-band short-brick T/R module based on the HTCC process, which realizes high-density integration of 8 Tx/Rx channels with a size of 36 mm×33 mm×3 mm. The T/R module has the functions of signal amplification, power dividing and synthesis, and amplitude and phase control. Through the planar transition and shielding design of microwave signals in HTCC substrate, the stable transmission of Ka-band microwave signals in high-density sub-cavities and the good amplitude and phase consistency between different channels are realized. The test results show that the T/R module has a receiving gain of ≥22 dB, a noise figure of ≤5.1 dB, and a transmit output power of ≥23 dBm, which can meet the application requirements of active phased array antennas for the new-generation communication, radar and other equipments.