The 19th National Congress of the Communist Party of China （hereafter， NCCPC） states that our economy has switched from the stage of high-speed to the stage of high-quality development. As the main participants of market economy， firms should change their conception of “To be bigger and comprehensive is better” into “Increasing value and efficiency”. Diversification is one of the ways of achieving in expansion and great-leap-forward development for firms， however， it’s sometimes labeled as “extensive development”. As an effective mechanism of internal monitoring and risk management， can internal control enhance the value of corporate diversification? Empirical evidence sampling from Non-SOEs listed in A-shares from 2007 to 2015 shows that the higher the quality of internal control is， the greater the value of corporate diversification will be， which confirms the optimizing role of internal control in selecting and implementing diversification strategy， and this effect is concentrated in the three major elements of internal control， Internal Environment，Control Activities and Information & Communication. After controlling the endogenous issues and conducting a series of robustness tests， our conclusion remains. Further， we don’t find there are such significant results in SOEs.