The thermal effects of Er/Yb-doped NaYF4 phosphor induced by 980/1510 nm laser diode irradiation were intuitively and contrastively investigated using an infrared thermal imaging technology with real-time online monitoring. The Yb3+/Er3+ codoped materials have strong thermal effects and high-temperature elevation under 980 nm irradiation. However, the severe thermal effects of materials with higher Er3+ ion doping concentration are remarkably attributed to the cross relaxation between the Er3+ ions under 980 nm irradiation. The energy transfer between Er3+ and Yb3+ ions in Er3+/Yb3+-codoped materials also contributes to the thermal effects under 1510 nm laser diode irradiation. Under the same testing conditions, the temperature elevation T of samples induced by 1510 nm laser diode irradiation is lower than that induced by 980 nm laser diode irradiation. The temperature rising rate and elevation T value of samples depend on the ion doping concentration and power density of the laser diode excitation. The internal temperature of the samples exhibits deep temperature gradient under 980/1510 nm laser diode irradiation. By comparing the two kinds of thermometry methods, the temperature value calculated by fluorescence intensity ratio is almost similar to that obtained through infrared thermal imaging technology under higher excitation power pumping.