A communications channel adaptation method for URLLC services which is executed in a communications system with at least a transmitter node (eNode) and a receiver or mobile terminal; wherein the receiver or mobile terminal measures the signal-to-interference ratio SIR from the reference signal received in instant t = i-1 and saves this SIR value,SIR i-1, in a memory; wherein based on this SIR value in instant t = i-1,SIR i-1, a CQI value, CQI i-1, is determined and sent to the transmitter node (eNode), which selects the modulation and coding format in the subsequent transmission (MCS i) in the downlink according to that CQI measured in instant t = i-1, CQI i-1; and wherein upon receiving in instant t = i the data packet sent by the transmitter node (eNode), the receiver terminal measures the SIR, SlR i, and saves it in a memory; wherein the method is characterized in that it comprises the steps of: calculating a variation quantification parameter of the communications channel,α i, defined as the difference existing between the channel quality taking as a reference the instant in which the CQI is determined by means of the reference signals, CQI i-1, and the instant in which the receiver mobile terminal receives the data corresponding to that CQI i-1 in the subsequent reception and measures the channel quality again, CQI i; calculating a correction margin, margin i, by means of a transformation function of two input parameters, which are the variation quantification parameter of the communications channel α i and a target reliability which is established for reliability index defined as: Reliability index = number of slots BLER i < BLER target total number of slots where BLERi i is the real instantaneous block error rate and BLER target is the target mean block error rate of a URLLC service required by the receiver or mobile terminal; correcting the SIR measured by the terminal in instant t = i,SIR i, by applying the calculated correction margin,margin i, such that the SIR corrected in instant t = i, SIR' i, is equal to the sum of the SIR in instant t = i, SlR i, plus the correction margin, margin i; and determining and sending to the transmitter node a corrected CQI, CQI' i, corresponding to that received and corrected signal-to-interference ratio, SIR' i, in instant t = i. wherein the receiver or mobile terminal measures the signal-to-interference ratio SIR from the reference signal received in instant t = i-1 and saves this SIR value,SIR i-1, in a memory; wherein based on this SIR value in instant t = i-1,SIR i-1, a CQI value, CQI i-1, is determined and sent to the transmitter node (eNode), which selects the modulation and coding format in the subsequent transmission (MCS i) in the downlink according to that CQI measured in instant t = i-1, CQI i-1; and wherein upon receiving in instant t = i the data packet sent by the transmitter node (eNode), the receiver terminal measures the SIR, SlR i, and saves it in a memory; wherein the method is characterized in that it comprises the steps of: calculating a variation quantification parameter of the communications channel,α i, defined as the difference existing between the channel quality taking as a reference the instant in which the CQI is determined by means of the reference signals, CQI i-1, and the instant in which the receiver mobile terminal receives the data corresponding to that CQI i-1 in the subsequent reception and measures the channel quality again, CQI i; calculating a correction margin, margin i, by means of a transformation function of two input parameters, which are the variation quantification parameter of the communications channel α i and a target reliability which is established for reliability index defined as: Reliability index = number of slots BLER i < BLER target total number of slots where BLERi i is the real instantaneous block error rate and BLER target is the target mean block error rate of a URLLC service required by the receiver or mobile terminal; correcting the SIR measured by the terminal in instant t = i,SIR i, by applying the calculated correction margin,margin i, such that the SIR corrected in instant t = i, SIR' i, is equal to the sum of the SIR in instant t = i, SlR i, plus the correction margin, margin i; and determining and sending to the transmitter node a corrected CQI, CQI' i, corresponding to that received and corrected signal-to-interference ratio, SIR' i, in instant t = i.