There are several instruments with which wellbore fluid pressure and flow parameters can be measured during underbalanced drilling(UBD). However, the real-time formation pressure test while drilling is yet a great challenge. Therefore, a much more precise pressure control drilling is not easy to be achieved. In this paper, technological methods and procedures are developed to obtain not only wellbore fluid pressure but also formation pressure while underbalanced drilling. Based on real-time pressure and fluids measuring during underbalanced drilling, methods to evaluate formation parameters such as permeability, porous media types and potential productivity are also developed. First, the pressure-while-drilling (PWD) methods, wellbore pressure calculation models and wellbore pressure rapid adjustment procedures are applied to get much more precise wellbore pressure profile and formation pressure while underbalanced drilling. Next, a surface real-time detection system is developed to detect the flux and fluid compositions while underbalanced drilling. Third, interpretation methods to evaluate formation parameters such as permeability, porous media types and potential productivity are also developed. These methods has been applied in three underbalanced drilling wells, one is a horizontal well and the others are vertical wells, which proved their significance at the first stage and reveal its potential in precise pressure control and formation parameters evaluation while underbalanced drilling.