An advection fog forecasting system, comprising two or more LoRa base stations, a weather data port for receiving weather data, and a data analysis server; the LoRa base stations each being configured to transmit and receive radio signals, to collect a strength indicator RSSI 1 of the actually received radio signal, and to transmit the radio signal strength indicator RSSI 1 to the data analysis server, wherein the LoRa base stations are built in a forecasting region, and a distance between two adjacent said LoRa base stations is of 5-100km; the weather data port being configured to receive weather data collected in the forecasting region, and to transmit the weather data to the data analysis server, wherein the weather data include a humidity, a wind speed and a rainfall; and the data analysis server being configured to determine an advection fog state between two said LoRa base stations according to the received weather data and the radio signal strength indicator RSSI 1 of the radio signal transmitted and received between the two LoRa base stations, wherein when the RSSI 1 is smaller than a forecasting threshold RSSI 0 and there is no rain in the forecasting region, it is determined that advection fog is present in an area of the forecasting region defined between two said LoRa base stations, and an advection fog density is to be obtained; in which the advection fog density is obtained using an equation of: W = R ̅ ∩ RSSI 1 − RSSI 0 where, R is the rainfall, and when R≠0, the advection fog density is 0; and when R=0, the advection fog density is W, or a difference between RSSI 1 and RSSI 0; in which the forecasting threshold is determined using an evaluation model that RSSI 0 = α + Log based d − Log basex X − Log basey Y where α is an RSSI signal distance adjustment parameter; d is the distance between two said LoRa base stations; based is a base for a logarithm of the distance between the LoRa base stations in the forecasting region; basex is a base for a logarithm of an adjustment factor for the humidity in the forecasting region; X is a value of the humidity in the forecasting region, basey is a base for a logarithm of an adjustment factor for the wind speed in the forecasting region; and Y is a value of the wind speed in the forecasting region. the LoRa base stations each being configured to transmit and receive radio signals, to collect a strength indicator RSSI 1 of the actually received radio signal, and to transmit the radio signal strength indicator RSSI 1 to the data analysis server, wherein the LoRa base stations are built in a forecasting region, and a distance between two adjacent said LoRa base stations is of 5-100km; the weather data port being configured to receive weather data collected in the forecasting region, and to transmit the weather data to the data analysis server, wherein the weather data include a humidity, a wind speed and a rainfall; and the data analysis server being configured to determine an advection fog state between two said LoRa base stations according to the received weather data and the radio signal strength indicator RSSI 1 of the radio signal transmitted and received between the two LoRa base stations, wherein when the RSSI 1 is smaller than a forecasting threshold RSSI 0 and there is no rain in the forecasting region, it is determined that advection fog is present in an area of the forecasting region defined between two said LoRa base stations, and an advection fog density is to be obtained; in which the advection fog density is obtained using an equation of: W = R ̅ ∩ RSSI 1 − RSSI 0 where, R is the rainfall, and when R≠0, the advection fog density is 0; and when R=0, the advection fog density is W, or a difference between RSSI 1 and RSSI 0; in which the forecasting threshold is determined using an evaluation model that RSSI 0 = α + Log based d − Log basex X − Log basey Y where α is an RSSI signal distance adjustment parameter; d is the distance between two said LoRa base stations; based is a base for a logarithm of the distance between the LoRa base stations in the forecasting region; basex is a base for a logarithm of an adjustment factor for the humidity in the forecasting region; X is a value of the humidity in the forecasting region, basey is a base for a logarithm of an adjustment factor for the wind speed in the forecasting region; and Y is a value of the wind speed in the forecasting region.