The thermal decomposition processes of 2,2,2-trinitroethyl-N-nitromethyl amine(TNMA), bis(2,2,2-trinitroethyl-N-nitro)ethylene diamine(BTNEDA) and 2,2,2-trinitroethyl-4,4,4-trinitrobutyrate(TNETB) under the conditions of vacuum,high loading density at low temperature and low loading density at high temperature were studied by using a highly sensitive Bourdon glass membrane manometer. The characteristic data, induction period(t_in), half decomposition period(t_1/2), initial decomposition rate(W₀), maximum decomposition rate(W_M), and time to maximum decomposition rate (t_M) at different temperatures for the thermal decomposition reaction of TNMA,BTNEDA and TNETB were obtained from the obtained standard volume of gas evolved (V_H) and decomposition rate (dV_H/dt) vs time (t) curves. The values of apparent activation energy E_a obtained by differential and integral isoconversional non-linear methods were used to check the validity of the values of apparent activation energy E_a obtained by plotting lgt_in, lgt_1/2 , lgW₀ , lgW_M and lgtM against 1/T. The results show that the relative error between the values of E_a and E_a corresponding to each characteristic datum is within ±10%.