The invention provides a range hood cleaning reminding system and method and a variable-frequency range hood, and relates to the technical field of range hoods, the system comprises an oil screen, a fan and a smoke exhaust assembly which are connected in sequence, a variable-frequency control driving unit connected with the fan, and a user interaction module connected with the variable-frequency control driving unit. The user interaction module receives an exhaust gear instruction input by a user, the frequency conversion control driving unit obtains a first fan operation parameter, corresponding to an exhaust gear represented by the exhaust gear instruction, of the fan, and calculates a difference value between a preset second fan operation parameter and the first fan operation parameter; when the difference value meets a preset reminding threshold value, a reminding instruction is sent to a user interaction module, and after the user interaction module receives the reminding instruction, a cleaning reminder corresponding to the oil net or the smoke exhaust assembly is sent to a user. The problem of poor user experience caused by too early or too late reminding is avoided, the timeliness and accuracy of oil screen cleaning reminding are improved, and the use experience of a user is improved.