In this paper,we explain the valuation issue of private equity investment.First,we briefly introduce the development history and research results of the portfolio problem.Then we discuss the research situation of the valuation issue of private equity investment in detail,including the portfolio selection of limited partners,as well as the research on the value evaluation system and evaluation methods of investment enterprises.And we give the model to be studied,namely the private equity model with unspanned risk.Finally,we give the expansion of the framework of the model under inflation,Knightian uncertainty and jump diffusion environment.