Main　steam　pressure　is　supposed　to　be　constant　in　traditional　power　system　simulation　software.　However,　this　leads　to　greater　generation　output　when　large　sources　(like　an　ultra　high　voltage　transmission　line)　are　lost,　which　in　turn　lead　to　higher　system　frequency　and　smaller　load　shedding　amount.　In　order　to　get　more　precise　frequency　locus,　a　boiler　model　should　be　used　in　simulation　software　after　large　power　source　is　lost.　Boiler　heat　storage　coefficient　in　the　model　can　be　got　after　primary　frequency　control　(PFC)　test　when　a　large　step　signal　is　used　as　disturbance　(input).　Since　turbine　valves　show　obvious　nonlinear　characteristic　for　large　opening　changing,　appropriate　method　should　be　used　to　eliminate　this　non-linear　characteristic　before　parameter　estimation　can　be　carried　out.　This　paper　shows　such　a　method.　Field　test　shows　that　turbine　parameters　and　the　boiler　heat　storage　coefficient　can　be　obtained　one　after　another.