The microlens image may serve deviations from the true projected centers and shape irregularities when the light field imaging system is used in narrow space. This paper analyzed and proposed the distortionless condition for microlens images. The narrow space is modeled as an additional aperture in the light field imaging system, whose pupil size and position in the light field imaging system were related to the distortionless condition. The distortionless condition was studied from three aspects and the experiments were designed including microlens image deviation and arithmetic aperture-shift. Experimental results show the correlation coefficient between the experimental and theoretical result is more than 99%, and aperture-shift measurement is (9.97±1.5) mm. The distortionless condition is proved by experimental results, which can be used to guide the design of light field imaging system and analyze the microlens image distortion parameters quantitatively.