Abstract: In order to study the connection between landscape formation of “red-bare soil” and soil erosion, ¹³⁷Cs change features of 3 different cover conditions under the same gradient were analyzed by the method of ¹³⁷Cs trace. The results showed that: the background value of ¹³⁷Cs was 878.41 Bq/m²; the distribution of ¹³⁷Cs in the profile of mountain-bare-soil was relatively shallow, which was within 15 cm usually. The soil erosion rate under the Yunnan pine forest land-cover was 1252.34 t/(km²·a) and it was 3069.718 t/(km²·a) under grass land-cover, the ¹³⁷Cs was not detected in the “red-bare soil”. The soil erosion rate followed the tendency of “red-bare-soil”＞grass＞pine forest. The worsening condition of mountain red earth land-cover was the fatal factor which contributed to the increase of soil erosion rate, soil erosion was the critical factor to the formation of “red-bare-soil”, and vegetation nursing was the key to control the formation of the “red-bare soil”.