Soil total nitrogen content is an important soil fertility parameter. However, the existed portable detector of soil total nitrogen content had several deficiencies, such as weak light intensity and low signal-to-noise ratio. Hence, a new portable soil total nitrogen content detector was designed based on high intensity light source and special optical fiber. Six sensitive wavelengths were used, which were 1108nm,1248nm, 1336nm, 1450nm, 1537nm and 1696nm. A high-power tungsten halogen lamp was used as the light source to improve the signal intensity, and one-way incident optical channel and six-way reflected optical channel were realized by using a “one-six” special optical fiber. The performance test of the detector showed that the conditioning circuit and the tungsten halogen lamp source worked stably, and the tungsten halogen lamp had higher measurement accuracy than the LED as the active light source. The prediction model was established by the absorbance values of the detector and the soil total nitrogen standard value. The highest model accuracy was obtained from a PLS model. The calibration R2C of the model was 0.8613 and the verification R2V of the model was 0.8042, which showed that the model had high precision and could be used for detector model embedding. A field experiment was conducted and the correlation coefficient between the real-time measurement result of the detector and the soil total nitrogen standard value reached 0.8280. The detector had high measurement accuracy and can meet the purpose of fast and accurate detection of the soil total nitrogen content in the field.