Experimental investigation of an L-band bifrequency（BF） magnetically insulated transmission line oscillator（MILO） based on azimuthal partition of cavity-depth, is carried out for the first time. Experimental system and measurement system of the BFMILO are set up. Far-field patterns of the antenna of the L-band BFMILO are obtained, and the total microwave power is obtained by integral of the power density of radiation field. Employing an electron beam of 420kV, 34kA, an L-band BFMILO can generate high power microwave （HPM） with two stable and separate frequencies. They are 1.26GHz and 1.45GHz respectively with power of 398MW and 222MW. Preliminary experimental results of BFMILOs with different azimuthal partition proportion are presented. The investigation proves the feasibility that BFMILO can generate HPM with two stable frequencies, which indicates an L-band BFMILO is developed successfully for the first time. A new direction of HPM investigations is pointed out.