A new type of portable multispectral imager consisting of off the Shelf focal plane arrays CCD camera,camera lens and Liquid Crystal Tunable Filter (LCTF) is presented.The LCTF used as a dispersion element is placed between the camera lens and CCD.This multispectral imager can perform multispectral image data acquisition experiment under active and passive illuminating condition,the spectrum range is 400~720 nm,and the spectral resolution is 10 nm.The numerical model of multispectral image acquisition is formulated,and the source of error is analyzed.A multispectral image data acquisition experiment under natural lighting condition is carried out,the target is a plant in pot,a multispectral image datacube is constructed and the spectrum of typical object point is illustrated.