The invention relates to a temperature-sensitive resistor, comprising: a wafer-shaped temperature-sensitive resistor chip; a circular-sheet-shaped sealing box comprising a circular-ring-shaped temperature-sensitive resistor accommodating device, a circular-sheet-shaped upper sealing cover and a circular-sheet-shaped lower sealing cover; the circular-sheet-shaped upper sealing cover seals the upperopening of the circular-ring-shaped temperature-sensitive resistor accommodating device; the circular-sheet-shaped lower sealing cover seals the lower opening of the circular-ring-shaped temperature-sensitive resistor accommodating device; the circular-ring-shaped accommodating device comprises a circular-ring-shaped main body; at least three uniformly annularly distributed blind holes are arranged in the inner side wall of the circular-ring-shaped main body; and a temperature-sensitive resistor chip holding device is arranged in the blind holes. A method for assembling a temperature sensor and a temperature-sensitive resistor is also provided. The abovementioned temperature-sensitive resistor avoids degrading of performance with time, and the service life is prolonged.