Whether the skills of open-ended funds improve their performance has been paid close attention for a long time． Computing the excess returns of funds relative to the risk-free rate and to the self-reported benchmark rate，the paper considers the performance of 437 funds established before Jan.1st 2013． The empirical results based on the recent q-factor model and the daily data between Jan.1st 2005 and Dec.31st 2017 show that: (1) the q-factor model has a good explanation power for the excess returns of open-ended funds，(2) the performances of funds can be overestimated when the excess returns are computed by the risk-free rate， (3) the managers of open-ended funds have a weak power of stock selection and a relative good power of short term，rather than long term，timing selection，which can improve short-term fund performance to a certain extent，and (4) the open-ended funds prefer stocks with good profitability or high investment levels．