The quantum microwave measurement technology based on Rydberg atoms has developed rapidly and received widespread attention. It has shown significant advantages such as probe size independent of wavelength and broad spectrum measurement. Fiber-coupled vapor cell probe is one of the key technologies for portable quantum microwave measurement systems. The existing two-port fiber-coupled probe shares the graded index (GRIN) lens and optical fibers for outputting detection light with inputting coupling light, which limits light transmission efficiency of the detection light to 17%. Under these conditions, the power of the inputting detection light must be increased to ensure sufficient power to output the detection light, causing the electromagnetically-induced transparency (EIT) spectrum to broaden to 11 MHz, ultimately resulting in reduced measurement sensitivity. In this work, we propose a three-port fiber-coupled atomic gas chamber probe with an integrated dichroic mirror. On condition that the detection light and coupling light are transmitted in opposite directions and overlap in the vapor cell, the outgoing detection light is separated into two beams; one goes to an individual GRIN lens and the other to the output fiber, and the detection light transmission efficiency is 40.4%, and the half-height width of the EIT spectrum is reduced to 6 MHz. The probe is used to measure the microwave electric field intensity and phase; its effectiveness is verified by its ability to receive QPSK, 16QAM digitally modulated signals.