Abstract: Temperature of every month on both the upper and lower bounds of subalpine dark conifer forests at various sites in China are estimated in terms of their distributions and temperature records,Based on these estimated data,the heat factor to influence and control the distribution and growth of sub-alpine dark conifer forests in China are discussed.It is found that the most important heat index to influence and control the distribution and growth of sub-alpine dark conifer forests is neither the mean temperaure in the warmest month,nor the maximum or minimum temperatures,but accumulated temperature of >0℃ monthly temperature or effective accumulated temperature of >5℃ monthly temperature. When accumulated temperature of >0℃ monthly temperature is more than 40℃, or effective accumulated temperature of >5℃ monthly temperature is over 50℃, sub-alpine dark conifer forests cannot grow well.When accumulated temperature of >0℃ monthly temperature is less than 30℃,or effective accumulated temperature of >5℃ monthly temperature is more than 60℃,sub-alpine dark conifer forests cannot grow at all.When effective accumulated temperature of >5℃ monthly temperature is between 15℃-45℃,sub-alpine dark conifer forests in China can grow well.The ecological significance of temperature in May and September,and in summer half year are discussed.