Thermal therapy is an approach applied in cancer treatment by heating local tissue to kill the tumor cells, which requires a high sensitivity of temperature monitoring during therapy. Current clinical methods like fMRI，near infrared or ultrasound for temperature measurement still have limitations on penetration depth or sensitivity. Photoacoustic temperature sensing is a newly developed temperature sensing method that has a potential to be applied in thermal therapy, which usually employs a single wavelength laser for signal generating and temperature detecting. Because of the system disturbances including laser intensity, ambient temperature and complexity of target, the accidental errors of measurement is unavoidable. For solving these problems, we proposed a new method of photoacoustic temperature sensing by using two wavelengths to reduce random error and increase the measurement accuracy in this paper. Firstly a brief theoretical analysis was deduced. Then in the experiment, a temperature measurement resolution of about 1℃ in the range of 23-48℃ in ex vivo pig blood was achieved, and an obvious decrease of absolute error was observed with averagely 1.7℃ in single wavelength pattern while nearly 1℃ in dual-wavelengths pattern. The obtained results indicates that dual-wavelengths photoacoustic sensing of temperature is able to reduce random error and improve accuracy of measuring, which could be a more efficient method for photoacoustic temperature sensing in thermal therapy of tumor.