The spatial resolution is a measurement of the image details

and is also an indictor for the objects details

it appears the degree of the scene details. But up to now

there are no effective approaches to be quantifiable evaluating the image resolution. The manner of forming an image can be in two ways: scanning manner and non-scanning manner （for example: framing）. In normal

forming an image by non-scanning manner has the same spatial resolution in the vertical and horizontal directions. But an image by scanning manner has the different spatial resolution in the two directions. The factors that influence the image spatial resolution exist: the contrast

shape

number of the scene which was observed and the lens

focus and instantaneous field of view（IFOV） of imaging system

the wavelength of radiation

aperture of imaging

model of image and the design of the imaging system

and so on. The main effective factors are distinguishing limit decided by the diffraction of the light

MTF（Modulate Transfer Function） of the imaging system

NSR（Noise Signal Ratio） and the design of imaging system. This paper is based on the entropy theory and the property of image information

bring forward the principle theory of varied information entropy

provided the conception

definition

method and character analysis. The experiment for bar images and remote sensing images of tsunami area approved that the method can be qualified to measure the spatial resolution in horizontal and vertical directions for the varied information equably

and provide a new method for the qualified measuring the image spatial resolution.