The present disclosure relates to a device, method and system for calculating, estimating, or monitoring the physiological parameters of a subject. At least one processor, when executing instructions, may perform one or more of the following operations. A first signal representing a pulse wave relating to heart activity of a subject may be received. A plurality of second signals representing time-varying information on the pulse wave may be received. A blood oxygen level of the subject based on the plurality of second signals may be determined. A first feature in the first signal may be identified. A second feature in one of the plurality of second signals may be identified. A pulse transit time based on a difference between the first feature and the second feature may be computed. A blood pressure of the subject may be calculated based on the pulse transit time.