The invention discloses a regulating method for imaging contrast of a scanning polarization force microscope. The method comprises the steps of preparing a nano-material on surface of a substrate, thereby obtaining a to-be-tested sample; making relative humidity of a testing environment gradually change in a range of 10%-90%, performing representation testing on the to-be-tested sample by means of the scanning polarization force microscope, and obtaining a scanning polarization force microscope picture, wherein in the obtained picture, the apparent height of the nano-material changes along with change of the relative humidity, and furthermore change between a positive value and a negative value occurs; choosing the relative humidity when the appearance height of the nano-material is 0nm, and determining the relative humidity as a critical humidity point; and selecting the relative humidity lower than the critical humidity point as an appropriate testing humidity for the imaging contrast. The regulating method is used for obtaining a representation result with high stability, high accuracy and high repeatability, thereby facilitating image analysis. The invention further discloses another regulating method which can be used for obtaining a good representation testing result and be used for differentiating at least two nano-materials with same morphology and different electric properties.