A flow control valve for a construction machine is provided, which can constantly control a flow rate of hydraulic fluid supplied to a hydraulic actuator through a flow control spool in a spool. The flow control valve for a construction machine, having a valve body in which a supply passage communicating with a pump passage and actuator ports connected to a hydraulic actuator are formed, and a spool installed in the valve body to be shifted, includes a flow control spool shifted in the spool to variably control a cross-sectional area of a passage connected to the one actuator port if a flow rate of the hydraulic fluid that flows through the supply passage is higher than a set flow rate, a first passage formed on the spool to communicate with the supply passage and a second passage formed on the spool to communication with the one actuator port and having a cross-sectional area that is varied depending on the shifting of the flow control spool.