The invention discloses a control system and a control method for the inlet temperature of a liquefied natural gas motor. The control system comprises an ECU, temperature, pressure and flow sensor, a controllable heat exchanger, a primary temperature electric adjusting device and a secondary temperature electric adjusting device; the primary temperature electric adjusting device controls the flow rate of a motor coolant liquid to adjust the temperature of gaseous natural gas in a liquefied natural gas gasification device; the secondary temperature electric adjusting device controls the flow rate of the motor coolant liquid to conduct secondary adjustment on the temperature of the gaseous natural gas. The control method and the control method have the benefits that the liquefied natural gas motor has the suitable natural gas inlet temperature within the whole working range, the defects of over high discharge of FC and CO caused by over low inlet temperature under cold starting and low working condition, and bad dynamic property and over high discharge of NOx caused by over high inlet temperature under high working condition in the prior art are overcome, the pollutant discharge quantity is lowered, and dynamic property and economy are improved.