A ramped-amplitude cross-polarization (RAMP-CP) was applied to coal measurement by solid-state C-13 NMR. Usual CP pulse sequence consists of a H-1 90 degrees pulse, the CP pulses and data acquisition under high-power H-1 decoupling. In the RAMP-CP pulse sequence in this study, C-13 spin-lock amplitude was changed Linearly during CP while H-1 spin-lock amplitude was constant. The parameters for RAMP-CP/MAS measurement, Delta omega(1C) (the change in the field strength of the spin-lock for C-13) and total contact time, were estimated for Upper Freeport coal using solid-state C-13 NMR. The results show that the signal intensity of the coal can be increased compared with the usual CP/MAS method by using the RAMP-CP/MAS method. Under the condition that the H-1 field strength was at 62.5 kHz, by using RAMP-CP/MAS method, the signal intensity of Upper Freeport coal increased compared with the CP/MAS method at Delta omega(1C) = 0.625-3.125 kHz and the total contact time was 2 ms.