Based on the general expression for spectral-angular distribution of the radiation emitted by a charged particle moving in exterior medium, the essential role of stationary phase points in Čerenkov effect is investigated. And the stationary phase method of calculating spectral-angular distribution of Čerenkov radiation from a charged particle moving in curved path is proposed. By the stationary phase method, the asymptotic form of spectral-angular distribution of synchrotron-Čerenkov radiation is calculated, and the result indicates that the spectrum of synchrotron-Čerenkov radiation near critical angle c is quite different from that near the plane of particle's orbit.