A new approach to study the equation of state in finite-temperature QCD is proposed on the lattice. Unlike the conventional method in which the temporal lattice size $N_t$ is fixed, the temperature $T$ is varied by changing $N_t$ at fixed lattice sca
le. The pressure of the hot QCD plasma is calculated by the integration of the trace anomaly with respect to $T$ at fixed lattice scale. This $T$-integral method is tested in quenched QCD on isotropic and anisotropic lattices and is shown to give reliable results especially at intermediate and low temperatures.
