The invention discloses a device and a method for phase detection based on a direct type micromechanical microwave power sensor. The device comprises an adjustable digital phase shifter (12), a power combiner (16), the direct type micromechanical microwave power sensor (19) and a digital multimeter (20), a reference microwave signal Vref is connected with a first input port (14) of the power combiner, a to-be-detected signal Vx is connected with an input port (11) of the adjustable digital phase shifter, an output port (13) of the adjustable digital phase shifter is connected with a second input port (15) of the power combiner, an output port (17) of the power combiner is connected with an input port (18) of the direct type micromechanical microwave power sensor, and back holes (8) on the direct type micromechanical microwave power sensor (19) are connected with the digital multimeter (20). The objective of accurate detection of microwave signal phase position is realized by utilizing the method of power after combining a measuring reference signal with the to-be-detected signal after phase shifting by the adjustable digital phase shifter.