Abstract: The pseudo-thermal light produced by using a rotating ground glass illuminated by a laser beam is the most common light source in ghost imaging.In this paper, the effects of coherent time of pseudo-thermal light on the quality and imaging efficiency of ghost imaging are studied theoretically and experimentally. Theoretically, first of all, it is pointed out that the coherence of pseudo-thermal light field is caused by the rotation of ground glass, and based on the space-time stochastic properties of rotating ground glass, the second-order correlation function of ghost imaging with pseudo-thermal light is derived, and the analytical expressionfor the reconstructed correlated image is obtained. The results show that, under the condition that the exposure time of the detector is much less than that of the coherence time of pseudo-thermal light, the rotating speed of ground glass is not included in the expression for theghost image and has no effect on the reconstructed correlated image. Secondly, several time scales involved in ghost imaging are analyzed and the way to improve the imaging efficiency is investigated. Through analysis, it shows that the exposure time should be far less than the coherence time of pseudo-thermal, and the sampling interval should be greater than the coherent time as much as possible, which ensuresthat the intensity fluctuation of light field can be detected effectively inghost imaging, thusit ensures the imaging quality and improves the imaging efficiency. Experimentally, ghost imaging results are compared at different rotating speeds of ground glass and different sampling frame rates respectively. The results show that the rotating speed of ground glass has no significant effect on reconstructed correlated image, and the quality of ghost imaging is not significantly improved by multiple sampling in the same coherent time, thus the validity of the theory is verified.The study provides a new way to improve the quality and efficiency of ghost imaging.