diff --git a/app/src/main/assets/updateLog.md b/app/src/main/assets/updateLog.md
index 1de59413b..bd696f3fe 100644
--- a/app/src/main/assets/updateLog.md
+++ b/app/src/main/assets/updateLog.md
@@ -3,6 +3,9 @@
 * 关注合作公众号 **[小说拾遗]** 获取好看的小说。
 * 旧版数据导入教程：先在旧版阅读(2.x)中进行备份，然后在新版阅读(3.x)【我的】->【备份与恢复】，选择【导入旧版本数据】。
 
+**2021/05/12**
+* 修复预下载bug
+
 **2021/05/11**
 * 修复部分webDav bug
 * 修复图片太大时会崩溃的bug
diff --git a/app/src/main/java/io/legado/app/service/help/ReadBook.kt b/app/src/main/java/io/legado/app/service/help/ReadBook.kt
index 88e7e6fa3..31adc1e33 100644
--- a/app/src/main/java/io/legado/app/service/help/ReadBook.kt
+++ b/app/src/main/java/io/legado/app/service/help/ReadBook.kt
@@ -21,6 +21,7 @@ import kotlinx.coroutines.GlobalScope
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.launch
 import splitties.init.appCtx
+import kotlin.math.max
 import kotlin.math.min
 
 
@@ -141,9 +142,9 @@ object ReadBook {
                 GlobalScope.launch(Dispatchers.IO) {
                     val maxChapterIndex =
                         min(chapterSize - 1, durChapterIndex + AppConfig.preDownloadNum)
-                    for (i in 2..maxChapterIndex) {
+                    for (i in durChapterIndex.plus(2)..maxChapterIndex) {
                         delay(1000)
-                        download(durChapterIndex + i)
+                        download(i)
                     }
                 }
             }
@@ -171,11 +172,10 @@ object ReadBook {
                 }
                 loadContent(durChapterIndex.minus(1), upContent, false)
                 GlobalScope.launch(Dispatchers.IO) {
-                    val maxChapterIndex =
-                        min(chapterSize - 1, durChapterIndex + AppConfig.preDownloadNum)
-                    for (i in 2..maxChapterIndex) {
+                    val minChapterIndex = max(0, durChapterIndex - 5)
+                    for (i in durChapterIndex.minus(2) downTo minChapterIndex) {
                         delay(1000)
-                        download(durChapterIndex - i)
+                        download(i)
                     }
                 }
             }