Charge accumulations on the wall of the chunnels in field emission devices are analyzed with the Monte Carlo method. The chunnel's wall is dielectric, and secondary electrons are generated when electrons hit the chunnel's wall. Under the electron bombardment, the secondary emission induces charging on the wall. It is implied that in the field emission process, the upper part of the chunnel's inside wall is positively charged, while the lower part of the chunnel's inside wall and the chunnel's underside wall are negatively charged. Four models with different forms of chunnels are studied. We analyze the effect of charge accumulation in different models by comparing the potential distributions near the cathode and the current density distributions of the cathode, respectively. The results show that increasing the slope of the chunnels will reduce charge accumulations at the chunnel's underside wall. Also, the energy distributions of electrons arriving at the anode are analyzed, and it suggests that the chunnel's slope may decrease the ratio of primary electrons directly on the anode to all the electrons on the anode.