Ministry of Environment has been designated 69 accident prevent materials, of which explosiveness or acute toxity is strong so that would cause explosion or serious accidents, as substances requiring preparation for accidents in Chemical Management Act. Among them are toxic and spread out in short time 22 chemicals, which can cause serious damage to the human body and the environment. Prevent measure from chemical release is can be the best practice, however it is also important to estimate the effect distance and minimize the damage for emergency response. In this study, we selected hydrogen chloride and hydrogen fluoride for developing the simplified estimating method and equation to calculate effect distance. Also we calculated the effect distance for toxic endpoints of hydrogen chloride and hydrogen fluoride(release rate 0.001 ㎥/s ~ 10 ㎥/s) at different ground roughness(open country and urban) based on the worst/ alternative case scenario by using the ALOHA, KORA and PHAST programs. Finally, we find the dispersion trends and suggest a simplified quick estimate formula such as y=AxB (R² 0.95). The new method of this research will be easy and useful for estimating effect distance without simulating risk assessment tools.