In this paper, optical microfiber coupler (OMC) with wavelength scale of waist region which is obtained with two twisted optical fibers by direct draw method is manufactured and experimentally studied. Experimental results show that coupling capacity will almost disappear when the diameter of the waist region is less than 2.5 μm . And the OMC will serve as the four ports optical microfiber (FPOM) with the capacity of combining and splitting light. We analyze and distinguish the optical properties between OMC and FPOM by the method of online monitoring the sample drawing process，the stability measurement and the wavelength scanning. Especially, an all optical modulation method based on thermal effect caused by light absorption is adopted for measuring the optical modulation capacity of the OMC and FPOM. The stable optical transmission properties of the FPOM are verified, and the splitting ratio is almost insensitive to wavelength, temperature, transmission optical power fluctuation and other physical parameters. Such properties ensure that the FPOM can be utilized to multiplex and integrate micro photonic devices. The OMC with structure optimization can be employed to sense the temperature and vibration, as well as potentially being used as an all optical modulator.