This paper is aimed to solve the question that present seismic catalogs are incomplete. The authors improve the maximum likelihood method to estimate seismic hazard parameters, considering different accuracy and completeness. As an example, we calculated the seismic hazard parameters of Fen-Wei Seismic Belt and South Shaanxi Region. And based on it, we use single-parameter sensitivity analysis method and multi-parameter sensitivity analysis method to analyse and discuss the sensitivity of parameters and the uncertainty of result.