Introducing olfactory display in the virtual reality (VR) system brings the immersive experience to new heights. However, it is intractable to simulate olfactory features (such as the intensity and the direction) with multiple levels. Visual stimuli have been proved to dominate human perception among multiple sensors in virtual environments. If visual stimuli can be used to guide the olfactory sense in VR, the design of the olfactory display can be simpler but still able to provide olfactory experience with more diversity. To understand the visual-olfactory effect on different olfactory characteristics, a portable olfactory display that can control the intensity and direction of odors was developed. An experimental study was conducted to investigate cross-modal human perception, i.e. how the visually virtual odor representation in VR influences human perception of real odor produced by the proposed olfactory display. The results showed that the perception of odor intensity and directionality can be modulated by visually virtual odor representation.