The up-conversion luminescence phenomenon of TmP5O14 crystal at room temperature pumped by pulsed DCM dye laser is studied. It is found that there appear strong 450 and 360 nm and weak 347 nm fluorescences. Through careful experiment al investigation and theoritical analysis, we find that the 450 and 360 nm radiations are 1D2→3F4,3H6 two-photon upconversion fluorescence and 347 nm radiation is 1I6→3F4 three-photon fluorescence. The up-conversion process can be elucidated as follows: when a Tm3+ ion absorbs a first pumping photon and reaches the 3F2 state from the 3H6 bound state, the population of 3F2 state falls down rapidly to the 3H4, state due to the rather strong nonradiative relaxation. Then the excited state absorption from 3H4 to 1D2 takes place and the 360 nm two-photon up-conversion fluorescence from 1D2 state is appears. Meanwhile, there is a small possibility for energy transfer between 1D2 state and 3H4 state. It results in a converted population with respect to the 1I6 state and the 347 nm three-photon up-conversion fluorescence is appear, the up-con-version mechanism of which is a complicated process involving both the excited state absorption and the temperature of photons.